Enable SafeStack for CloudABI.

Summary:
I've got a patchset in my home directory to integrate support for
SafeStack into CloudABI's C library. All of the CloudABI unit tests
still seem to pass. Pretty sweet!

This change adds the necessary changes to Clang to make
-fsanitize=safe-stack work on CloudABI. Without it, passing this command
line flag throws an error.

Reviewers: eugenis, samsonov

Differential Revision: http://reviews.llvm.org/D17243

llvm-svn: 261135
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index 6c5cdb2..165d534 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -3000,6 +3000,12 @@
   return new tools::cloudabi::Linker(*this);
 }
 
+SanitizerMask CloudABI::getSupportedSanitizers() const {
+  SanitizerMask Res = ToolChain::getSupportedSanitizers();
+  Res |= SanitizerKind::SafeStack;
+  return Res;
+}
+
 /// OpenBSD - OpenBSD tool chain which can call as(1) and ld(1) directly.
 
 OpenBSD::OpenBSD(const Driver &D, const llvm::Triple &Triple,