For PR496:

For PR496:
When llvm-gcc is not available, bypass rules for Modules and Bytecode
Libraries that require llvm-gcc and emit instead a warning that llvm-gcc
is not available. This permits "make LLVMGCC=" to build LLVM completely
without error and provides warnings about the modules and bc libs that
could not be constructed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20185 91177308-0d34-0410-b5e6-96231b3b80d8