Revert of [GN]: BUILD file housecleaning

Revert of [GN]: BUILD file housecleaning (patchset #7 id:120001 of https://codereview.chromium.org/1368223002/ )

Also reverts roll of openmax_dl: 76e3b24427d1e33ad8912fdc85692f115e4ca41f


Reason for revert:
[721/14633] ASM obj/third_party/openmax_dl/dl/openmax_dl_armv7/omxSP_FFTInv_CCSToR_F32_Sfs_s.o
FAILED: /usr/local/google/home/agrieve/goma/gomacc ../../third_party/llvm-build/Release+Asserts/bin/clang -MMD -MF obj/third_party/openmax_dl/dl/openmax_dl_armv7/omxSP_FFTInv_CCSToR_F32_Sfs_s.o.d -DV8_DEPRECATION_WARNINGS -DCLD_VERSION=2 -DENABLE_NOTIFICATIONS -DENABLE_BROWSER_CDMS -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1 -DENABLE_SPELLCHECK=1 -DUSE_BROWSER_SPELLCHECKER=1 -DDONT_EMBED_BUILD_METADATA -DUSE_OPENSSL=1 -DUSE_OPENSSL_CERTS=1 -DNO_TCMALLOC -DDISABLE_NACL -DENABLE_CONFIGURATION_POLICY -DENABLE_SUPERVISED_USERS=1 -DENABLE_AUTOFILL_DIALOG=1 -DUSE_PROPRIETARY_CODECS -DV8_USE_EXTERNAL_STARTUP_DATA -DVIDEO_HOLE=1 -DMOBILE_SAFE_BROWSING -DSAFE_BROWSING_DB_REMOTE -DSAFE_BROWSING_SERVICE -DCHROMIUM_BUILD -DENABLE_MEDIA_ROUTER=1 -DENABLE_WEBVR -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=247874-1 -D_FILE_OFFSET_BITS=64 -DANDROID -DHAVE_SYS_UIO_H -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DCOMPONENT_BUILD -D__GNU_SOURCE=1 -D__compiler_offsetof=__builtin_offsetof -Dnan=__builtin_nan -D_DEBUG -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DWTF_USE_DYNAMIC_ANNOTATIONS=1 -DDL_ARM_NEON_OPTIONAL -I../.. -Igen -I../../third_party/openmax_dl -I../../third_party/android_tools/ndk/sources/android/cpufeatures -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -march=armv7-a -mfloat-abi=softfp -mthumb -mtune=generic-armv7-a -funwind-tables -fPIC -pipe -fcolor-diagnostics -mfpu=vfpv3-d16 --sysroot=/usr/local/google/home/agrieve/ssd/git/clankium1/src/third_party/android_tools/ndk/platforms/android-16/arch-arm -c ../../third_party/openmax_dl/dl/sp/src/arm/armv7/omxSP_FFTInv_CCSToR_F32_Sfs_s.S -o obj/third_party/openmax_dl/dl/openmax_dl_armv7/omxSP_FFTInv_CCSToR_F32_Sfs_s.o
clang: warning: argument unused during compilation: '-mfloat-abi=softfp'
clang: warning: argument unused during compilation: '-mthumb'
clang: warning: argument unused during compilation: '-mfpu=vfpv3-d16'
error: unknown target CPU 'armv7-a'

Original issue's description:
> [GN]: BUILD file housecleaning
> 
> + Turn on precompiled headers on Mac.
> + Change the toolchains to use asmflags instead of cflags and cflags_c.
> + Remove a TODO to hardcode the Mac SDK since the location of the SDK is not always guaranteed (on bots, for example).
> + GN: .S or .asm files no longer trigger cflags or cflags_c to be written to the ninja file.
> 
> BUG=none
> 
> Committed: https://crrev.com/7a73be6eb4963662a1e9455dcdab0d5130324901
> Cr-Commit-Position: refs/heads/master@{#351202}

TBR=brettw@chromium.org,andybons@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=none

[agrieve, 2015-09-30 14:12:51]

Created Revert of [GN]: BUILD file housecleaning