Subzero: Auto-detect cmake versus autoconf LLVM build.

Subzero: Auto-detect cmake versus autoconf LLVM build.

The CMAKE=1 option is no longer needed.

Pretty much all the tools we need are now in pnacl_newlib_raw/bin, so use PNACL_BIN_PATH set to that instead of using LLVM_BIN_PATH and BINUTILS_BIN_PATH.

However, for the autoconf build, libgtest and libtest_main and clang-format are only under the llvm_x86_64_linux_work directory, so they need special casing.  This also means that you have to actually do an LLVM build and not blow away the work directory in order to "make check-unit" or "make format".

BUG= none
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/1085733002