Explicitly set target_subarch for iOS on ia32/x64
Explicitly set target_subarch for iOS on ia32/x64

https://webrtc-codereview.appspot.com/48909004/ only fixed
the target_subarch problem for ARM. This fixes it for the
x86 targets that are used for the iOS simulator (ia32/x64).

BUG=4532
TESTED=Built locally using:
export GYP_DEFINES="build_with_libjingle=1 build_with_chromium=0 libjingle_objc=1 OS=ios target_arch=ia32"
export GYP_GENERATOR_FLAGS="$GYP_GENERATOR_FLAGS output_dir=out_sim"
export GYP_CROSSCOMPILE=1
gclient runhooks
ninja -C out_sim/Release-iphonesimulator iossim AppRTCDemo

R=tkchin@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/44159004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8991}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 529921e7cdbb391cf92d7a4a83341e412c1aee2f

sippet/webrtc,sippet/webrtc,sippet/webrtc,Alkalyne/webrtctrunk,krieger-od/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,sippet/webrtc,krieger-od/webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,Alkalyne/webrtctrunk,sippet/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,aleonliao/webrtc-trunk,krieger-od/webrtc,Alkalyne/webrtctrunk,aleonliao/webrtc-trunk,aleonliao/webrtc-trunk,aleonliao/webrtc-trunk,Alkalyne/webrtctrunk,sippet/webrtc,aleonliao/webrtc-trunk,krieger-od/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,krieger-od/webrtc,jchavanton/webrtc,jchavanton/webrtc,krieger-od/webrtc