Add EXPERIMENTAL --rtlib=compiler-rt to GNU Clang

This commit is not strictly correct nor accounts for all uses (shared
objects, for example), but it allows one to test the compiler-rt library
on GNU targets.

Using this patch to run the test-suite has already shown me problems
on ARM. Since this is a Darwin-only flag, nobody is using it, so it
shouldn't be a problem.

I will need extension to deal with the shared cases, but since we're
not compiling libclang_rt.so, that's not yet applicable. Many other
problems will have to be fixed first in compiler-rt (such as removing
the 'arch' name from it and making it trully multi-arch, moving it to
the default lib directory, make both .a and .so variants, etc).

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201307 91177308-0d34-0410-b5e6-96231b3b80d8
Remove spurious default case to silent sanitizer

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201309 91177308-0d34-0410-b5e6-96231b3b80d8
XCore target -fexceptions flag handling

XCore target has -fno-exception as the default option
Pass on "-fexceptions" flag to xcc (linker)

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201310 91177308-0d34-0410-b5e6-96231b3b80d8
add comment explaining previous commit

 see 'XCore target -fexceptions flag handling'

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201311 91177308-0d34-0410-b5e6-96231b3b80d8
XCore target pass -v flag to assembler & linker

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201312 91177308-0d34-0410-b5e6-96231b3b80d8
ARM & AArch64 NEON: share the vabs implementation.

This changes ARM to use @llvm.fabs for floating-point vabs. Patterns
already existed in the backend, and it might help mid-end phases since
it's more likely to be understood than @llvm.arm.neon.vabs.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201313 91177308-0d34-0410-b5e6-96231b3b80d8