HOST_linux-x86: Avoid doubly define macro _FORTIFY_SOURCE
HOST_linux-x86: Avoid doubly define macro _FORTIFY_SOURCE

While building Android with latest host gcc, it causes the following
build error:

Install: out/host/linux-x86/bin/mkbootimg
host C++: obbtool <= frameworks/base/tools/obbtool/Main.cpp
<command-line>:0:0: error: "_FORTIFY_SOURCE" redefined [-Werror]
<built-in>:0:0: note: this is the location of the previous definition
cc1plus: all warnings being treated as errors

In order to make build system happy, this patch does unset macro
_FORTIFY_SOURCE and then define it in host cflags.

Change-Id: Ic37a90f05081a2c3650b3335bc87e9e895900fb2

see4ri/lolili,xorware/android_build,hagar006/platform_manifest,xorware/android_build,RR-msm7x30/platform_manifest,knone1/platform_manifest,ND-3500/platform_manifest,xorware/android_build,fallouttester/platform_manifest,Hybrid-Power/startsync,xorware/android_build,xorware/android_build,pranav01/platform_manifest