Set CC and CXX for goma-clang even if ninja isn't explicitly set.
Set CC and CXX for goma-clang even if ninja isn't explicitly set.

It might be on implicitly. And setting CC and CXX for other build systems
doesn't hurt (make bakes it into the makefile but then uses the CC / CXX
env vars at build time, and xcode ignores it).

BUG=313318

Review URL: https://codereview.chromium.org/53923003

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@232031 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build