NaCl: Remove use of NACL_BUILD_* in common.gypi.
NaCl: Remove use of NACL_BUILD_* in common.gypi.

NACL_BUILD_ARCH and NACL_BUILD_SUBARCH are now supplied by build_config.h and
need not come from the build system.

TEST=Local build of chromium browser_tests on Linux x86_64, win_chromium_rel_ng trybot
BUG=https://code.google.com/p/chromium/issues/detail?id=440012

Review URL: https://codereview.chromium.org/902903002

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client