Allow GCC to build Skia on Mac.
Allow GCC to build Skia on Mac.

GCC doesn't understand -fasm-blocks or -mpascal-strings, but we don't care
about them.

While looking around in Gyp, I noticed a better way to disable warnings about
offsetof so that it doesn't tell us "disabling this warning makes no sense in C"
for every C source file we compile.

BUG=skia:

Review URL: https://codereview.chromium.org/650553002

chenlian2015/skia_from_google,VRToxin-AOSP/android_external_skia,MonkeyZZZZ/platform_external_skia,w3nd1go/android_external_skia,UBERMALLOW/external_skia,nvoron23/skia,noselhq/skia,aosp-mirror/platform_external_skia,AOSPB/external_skia,spezi77/android_external_skia,rubenvb/skia,Jichao/skia,nfxosp/platform_external_skia,Igalia/skia,YUPlayGodDev/platform_external_skia,VRToxin-AOSP/android_external_skia,AOSP-YU/platform_external_skia,timduru/platform-external-skia,rubenvb/skia,scroggo/skia,MarshedOut/android_external_skia,MarshedOut/android_external_skia,google/skia,chenlian2015/skia_from_google,MonkeyZZZZ/platform_external_skia,pcwalton/skia,boulzordev/android_external_skia,MarshedOut/android_external_skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,YUPlayGodDev/platform_external_skia,spezi77/android_external_skia,shahrzadmn/skia,BrokenROM/external_skia,nvoron23/skia,MarshedOut/android_external_skia,scroggo/skia,shahrzadmn/skia,PAC-ROM/android_external_skia,PAC-ROM/android_external_skia,DiamondLovesYou/skia-sys,shahrzadmn/skia,jtg-gg/skia,qrealka/skia-hc,AOSPB/external_skia,chenlian2015/skia_from_google,pcwalton/skia,AOSP-YU/platform_external_skia,w3nd1go/android_external_skia,MonkeyZZZZ/platform_external_skia,TeamTwisted/external_skia,YUPlayGodDev/platform_external_skia,PAC-ROM/android_external_skia,timduru/platform-external-skia,pcwalton/skia,pcwalton/skia,nfxosp/platform_external_skia,aosp-mirror/platform_external_skia,timduru/platform-external-skia,Infinitive-OS/platform_external_skia,aosp-mirror/platform_external_skia,vanish87/skia,samuelig/skia,samuelig/skia,AOSP-YU/platform_external_skia,TeamExodus/external_skia,Igalia/skia,YUPlayGodDev/platform_external_skia,MinimalOS-AOSP/platform_external_skia,jtg-gg/skia,Jichao/skia,boulzordev/android_external_skia,nfxosp/platform_external_skia,scroggo/skia,Infinitive-OS/platform_external_skia,vanish87/skia,BrokenROM/external_skia,nvoron23/skia,jtg-gg/skia,nfxosp/platform_external_skia,AOSPB/external_skia,aosp-mirror/platform_external_skia,amyvmiwei/skia,Igalia/skia,Infinitive-OS/platform_external_skia,shahrzadmn/skia,amyvmiwei/skia,VRToxin-AOSP/android_external_skia,MarshedOut/android_external_skia,UBERMALLOW/external_skia,chenlian2015/skia_from_google,geekboxzone/mmallow_external_skia,tmpvar/skia.cc,HalCanary/skia-hc,nfxosp/platform_external_skia,OneRom/external_skia,tmpvar/skia.cc,MinimalOS-AOSP/platform_external_skia,YUPlayGodDev/platform_external_skia,invisiblek/android_external_skia,scroggo/skia,boulzordev/android_external_skia,TeamExodus/external_skia,BrokenROM/external_skia,amyvmiwei/skia,HalCanary/skia-hc,todotodoo/skia,UBERMALLOW/external_skia,MarshedOut/android_external_skia,noselhq/skia,boulzordev/android_external_skia,w3nd1go/android_external_skia,Hikari-no-Tenshi/android_external_skia,qrealka/skia-hc,google/skia,YUPlayGodDev/platform_external_skia,VRToxin-AOSP/android_external_skia,spezi77/android_external_skia,pcwalton/skia,MarshedOut/android_external_skia,invisiblek/android_external_skia,geekboxzone/mmallow_external_skia,spezi77/android_external_skia,HalCanary/skia-hc,tmpvar/skia.cc,geekboxzone/mmallow_external_skia,BrokenROM/external_skia,shahrzadmn/skia,amyvmiwei/skia,w3nd1go/android_external_skia,nfxosp/platform_external_skia,samuelig/skia,VRToxin-AOSP/android_external_skia,MinimalOS-AOSP/platform_external_skia,DiamondLovesYou/skia-sys,TeamTwisted/external_skia,shahrzadmn/skia,HalCanary/skia-hc,TeamTwisted/external_skia,TeamTwisted/external_skia,vanish87/skia,AOSPB/external_skia,nvoron23/skia,UBERMALLOW/external_skia,invisiblek/android_external_skia,boulzordev/android_external_skia,w3nd1go/android_external_skia,Infinitive-OS/platform_external_skia,geekboxzone/mmallow_external_skia,Infinitive-OS/platform_external_skia,BrokenROM/external_skia,qrealka/skia-hc,invisiblek/android_external_skia,DiamondLovesYou/skia-sys,rubenvb/skia,shahrzadmn/skia,pcwalton/skia,jtg-gg/skia,invisiblek/android_external_skia,qrealka/skia-hc,Hikari-no-Tenshi/android_external_skia,Jichao/skia,pcwalton/skia,amyvmiwei/skia,TeamTwisted/external_skia,ominux/skia,TeamExodus/external_skia,AOSPB/external_skia,samuelig/skia,jtg-gg/skia,TeamExodus/external_skia,TeamExodus/external_skia,AOSPB/external_skia,ominux/skia,w3nd1go/android_external_skia,Hikari-no-Tenshi/android_external_skia,noselhq/skia,tmpvar/skia.cc,HalCanary/skia-hc,todotodoo/skia,OneRom/external_skia,rubenvb/skia,DiamondLovesYou/skia-sys,UBERMALLOW/external_skia,DiamondLovesYou/skia-sys,chenlian2015/skia_from_google,aosp-mirror/platform_external_skia,nvoron23/skia,OneRom/external_skia,scroggo/skia,shahrzadmn/skia,PAC-ROM/android_external_skia,Jichao/skia,timduru/platform-external-skia,rubenvb/skia,OneRom/external_skia,amyvmiwei/skia,vanish87/skia,nvoron23/skia,YUPlayGodDev/platform_external_skia,OneRom/external_skia,spezi77/android_external_skia,amyvmiwei/skia,YUPlayGodDev/platform_external_skia,timduru/platform-external-skia,google/skia,MonkeyZZZZ/platform_external_skia,ominux/skia,todotodoo/skia,MonkeyZZZZ/platform_external_skia,DiamondLovesYou/skia-sys,noselhq/skia,scroggo/skia,MonkeyZZZZ/platform_external_skia,noselhq/skia,ominux/skia,AOSP-YU/platform_external_skia,Igalia/skia,geekboxzone/mmallow_external_skia,todotodoo/skia,MinimalOS-AOSP/platform_external_skia,Igalia/skia,TeamTwisted/external_skia,todotodoo/skia,Jichao/skia,ominux/skia,invisiblek/android_external_skia,google/skia,vanish87/skia,HalCanary/skia-hc,ominux/skia,UBERMALLOW/external_skia,boulzordev/android_external_skia,google/skia,VRToxin-AOSP/android_external_skia,MarshedOut/android_external_skia,Jichao/skia,rubenvb/skia,geekboxzone/mmallow_external_skia,AOSP-YU/platform_external_skia,amyvmiwei/skia,chenlian2015/skia_from_google,UBERMALLOW/external_skia,MonkeyZZZZ/platform_external_skia,AOSP-YU/platform_external_skia,AOSP-YU/platform_external_skia,UBERMALLOW/external_skia,BrokenROM/external_skia,tmpvar/skia.cc,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,Jichao/skia,ominux/skia,BrokenROM/external_skia,TeamTwisted/external_skia,Jichao/skia,OneRom/external_skia,nfxosp/platform_external_skia,PAC-ROM/android_external_skia,MinimalOS-AOSP/platform_external_skia,PAC-ROM/android_external_skia,rubenvb/skia,UBERMALLOW/external_skia,rubenvb/skia,qrealka/skia-hc,noselhq/skia,geekboxzone/mmallow_external_skia,noselhq/skia,Infinitive-OS/platform_external_skia,YUPlayGodDev/platform_external_skia,MinimalOS-AOSP/platform_external_skia,jtg-gg/skia,nvoron23/skia,google/skia,tmpvar/skia.cc,TeamExodus/external_skia,ominux/skia,PAC-ROM/android_external_skia,chenlian2015/skia_from_google,nfxosp/platform_external_skia,scroggo/skia,noselhq/skia,TeamExodus/external_skia,google/skia,TeamExodus/external_skia,google/skia,todotodoo/skia,VRToxin-AOSP/android_external_skia,tmpvar/skia.cc,MinimalOS-AOSP/platform_external_skia,VRToxin-AOSP/android_external_skia,geekboxzone/mmallow_external_skia,pcwalton/skia,aosp-mirror/platform_external_skia,AOSP-YU/platform_external_skia,OneRom/external_skia,w3nd1go/android_external_skia,aosp-mirror/platform_external_skia,BrokenROM/external_skia,scroggo/skia,MonkeyZZZZ/platform_external_skia,w3nd1go/android_external_skia,Igalia/skia,vanish87/skia,timduru/platform-external-skia,Hikari-no-Tenshi/android_external_skia,google/skia,AOSPB/external_skia,nvoron23/skia,Igalia/skia,qrealka/skia-hc,MarshedOut/android_external_skia,todotodoo/skia,nfxosp/platform_external_skia,qrealka/skia-hc,aosp-mirror/platform_external_skia,samuelig/skia,samuelig/skia,PAC-ROM/android_external_skia,vanish87/skia,ominux/skia,shahrzadmn/skia,TeamExodus/external_skia,MonkeyZZZZ/platform_external_skia,jtg-gg/skia,OneRom/external_skia,OneRom/external_skia,Infinitive-OS/platform_external_skia,Igalia/skia,pcwalton/skia,todotodoo/skia,vanish87/skia,rubenvb/skia,spezi77/android_external_skia,todotodoo/skia,invisiblek/android_external_skia,Jichao/skia,Hikari-no-Tenshi/android_external_skia,AOSPB/external_skia,boulzordev/android_external_skia,invisiblek/android_external_skia,Infinitive-OS/platform_external_skia,rubenvb/skia,HalCanary/skia-hc,AOSP-YU/platform_external_skia,noselhq/skia,boulzordev/android_external_skia,aosp-mirror/platform_external_skia,Infinitive-OS/platform_external_skia,AOSPB/external_skia,tmpvar/skia.cc,DiamondLovesYou/skia-sys,geekboxzone/mmallow_external_skia,TeamTwisted/external_skia,tmpvar/skia.cc,MinimalOS-AOSP/platform_external_skia,timduru/platform-external-skia,samuelig/skia,qrealka/skia-hc,MinimalOS-AOSP/platform_external_skia,samuelig/skia,PAC-ROM/android_external_skia,VRToxin-AOSP/android_external_skia,boulzordev/android_external_skia,google/skia,HalCanary/skia-hc,w3nd1go/android_external_skia,vanish87/skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,nvoron23/skia,TeamTwisted/external_skia