This is for cross platform support. gyp_packager.py is modified
from build/gyp_chromium and adapted to packager code.
New build instructions:
1. Setup gyp: ./gyp_packager.py
clang is not enabled by default, which can be enabled by overriding
GYP_DEFINE environment variable, i.e. "GYP_DEFINES='clang=1
use_openssl=1' ./gyp_packager.py".
Ninja is the default build system. User can also change to make by
overriding GYP_GENERATORS to make, i.e. "GYP_GENERATORS='make'
./gyp_packager.py".
2. The first step generates the make files but does not start the
build process. Ninja is the default build system. Refer to Ninja
manual on how to do the build.
Common syntaxes: ninja -C out/{Debug/Release} [Module]
Module is optional. If not specified, build everything.
Step 1 is only required if there is any gyp file change. Otherwise, you
may just run ninja.
Change-Id: I89cade7278bfdd3992644457e896e5a10085568b
Kongqun Yang