Remove erroneous uses of CXX / CXX_target / CXX_host from gyp.

The current gyp config tries to test whether the compiler is an arm / mips
compiler and whether it supports -m32 / -m64 based on a test within gyp.
Unfortunately CXX / CXX_target / CXX_host are no no longer set early enough
in gyp for this to work, and so all of these tests were actually being done
using "$(which g++)" rather than the appropriate CXX_target / CXX_host compiler.

This change removes these dynamic tests and instead bases the decisions on
knowledge of the host / target / v8_target architecture combination.  The
the -m32/-m64 flags are set based on host_cxx_is_biarch / target_cxx_is_biarch,
which are set to reasonable defaults of only ia32/x64 or clang compilers
being build for biarch support.  The host_cxx_is_biarch / target_cxx_is_biarch
variables can be overriden if required.

BUG=384474
LOG=NO
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/382343003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22425 ce2b1a6d-e550-0410-aec6-3dcde31c8c00