Add //build/config/BUILD.gn to exec whitelist for GN.

Add //build/config/BUILD.gn to exec whitelist for GN.

Affected Linux GN build, not Windows.

R=kjellander@chromium.org
BUG=libyuv:583
TESTED=gn gen out/Debug --args=is_debug=true

Committed: https://chromium.googlesource.com/libyuv/libyuv/+/ddbc63f7b994680effe8d2c7ad3dd71c00251d37

[kjellander_chromium, 2016-04-06 18:22:48]

lgtm

[fbarchard1, 2016-04-06 18:23:31]

Description was changed from

==========
Add //build/config/BUILD.gn to exec whitelist for GN.

Affected Linux GN build, not Windows.

R=kjellander@chromium.org
BUG=libyuv:583
TESTED=gn gen out/Debug --args=is_debug=true
==========

to

==========
Add //build/config/BUILD.gn to exec whitelist for GN.

Affected Linux GN build, not Windows.

R=kjellander@chromium.org
BUG=libyuv:583
TESTED=gn gen out/Debug --args=is_debug=true

Committed:
https://chromium.googlesource.com/libyuv/libyuv/+/ddbc63f7b994680effe8d2c7ad3...
==========

[fbarchard1, 2016-04-06 18:23:32]

Committed patchset #1 (id:1) manually as
ddbc63f7b994680effe8d2c7ad3dd71c00251d37 (presubmit successful).

[fbarchard1, 2016-04-06 18:30:35]

Note to self - update README.md to show gn build on linux.
same as windows but no 'call'
See Also
https://www.chromium.org/developers/gn-build-configuration

is_official_build = true
is_chrome_branded = true
is_debug = false

There are 3 configs commonly built: debug, release, official.  For official:
gn gen out/Release "--args=is_debug=false is_official_build=true
is_chrome_branded=true"
ninja -v -C out/Release

A sample verbose compile:
[228/239] ../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF
obj/libyuv/scale_gcc.o.d -DHAVE_JPEG -DV8_DEPRECATION_WARNINGS -DCLD_VERSION=2
-DENABLE_MDNS=1 -DENABLE_NOTIFICATIONS -DENABLE_PEPPER_CDMS -DENABLE_PLUGINS=1
-DENABLE_PDF=1 -DENABLE_PRINTING=1 -DENABLE_BASIC_PRINTING=1
-DENABLE_PRINT_PREVIEW=1 -DENABLE_SPELLCHECK=1 -DUSE_UDEV
-DUI_COMPOSITOR_IMAGE_TRANSPORT -DUSE_AURA=1 -DUSE_PANGO=1 -DUSE_CAIRO=1
-DUSE_CLIPBOARD_AURAX11=1 -DUSE_DEFAULT_RENDER_THEME=1 -DUSE_GLIB=1
-DUSE_OPENSSL=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DENABLE_WEBRTC=1
-DENABLE_EXTENSIONS=1 -DENABLE_CONFIGURATION_POLICY -DENABLE_TASK_MANAGER=1
-DENABLE_THEMES=1 -DENABLE_CAPTIVE_PORTAL_DETECTION=1 -DENABLE_SESSION_SERVICE=1
-DENABLE_APP_LIST=1 -DENABLE_SETTINGS_APP=1 -DENABLE_SUPERVISED_USERS=1
-DENABLE_SERVICE_DISCOVERY=1 -DENABLE_AUTOFILL_DIALOG=1 -DENABLE_TOPCHROME_MD=1
-DUSE_PROPRIETARY_CODECS -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD
-DSAFE_BROWSING_DB_LOCAL -DOFFICIAL_BUILD -DGOOGLE_CHROME_BUILD
-DENABLE_MEDIA_ROUTER=1 -DCR_CLANG_REVISION=261368-1 -D_FILE_OFFSET_BITS=64
-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DNO_UNWIND_TABLES -DNDEBUG
-DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DUSE_LIBJPEG_TURBO=1 -I../.. -Igen
-I../.. -I../../include -I../../third_party/libjpeg_turbo -fno-strict-aliasing
--param=ssp-buffer-size=4 -fstack-protector -fno-unwind-tables
-fno-asynchronous-unwind-tables -fPIC -pipe
-B../../third_party/binutils/Linux_x64/Release/bin -fcolor-diagnostics
-fdebug-prefix-map=/usr/local/google/home/fbarchard/build/libyuv/libyuv=.
-pthread -m64 -march=x86-64 -O2 -fno-ident -fdata-sections -ffunction-sections
-g2 --sysroot=../../build/linux/debian_wheezy_amd64-sysroot -fvisibility=hidden
-Xclang -load -Xclang
../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so -Xclang
-add-plugin -Xclang find-bad-constructs -Xclang -plugin-arg-find-bad-constructs
-Xclang check-templates -Xclang -plugin-arg-find-bad-constructs -Xclang
follow-macro-expansion -Wheader-hygiene -Wstring-conversion -Wall
-Wno-unused-variable -Werror -Wno-missing-field-initializers
-Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default
-Wno-deprecated-register -Wno-unneeded-internal-declaration
-Wno-inconsistent-missing-override -Wno-shift-negative-value
-fno-threadsafe-statics -fvisibility-inlines-hidden -std=gnu++11 -fno-rtti
-fno-exceptions -Wno-deprecated -c ../../source/scale_gcc.cc -o
obj/libyuv/scale_gcc.o