[CUDA] Forward sanitizer support to host toolchain

[jhen]

Summary

This is an improvement on rL288448 where address sanitization was listed
as supported for the CudaToolChain. Since the intent is for the
CudaToolChain not to reject any flags supported by the host compiler,
this patch switches to forwarding the CudaToolChain sanitizer support to
the host toolchain rather than explicitly whitelisting address
sanitization.

Thanks to hfinkel for this suggestion.

[jlebar]

I like it!

[hfinkel]

LGTM

cfe/trunk/lib/Driver/ToolChains.cpp

 }
 
 void CudaToolChain::AddIAMCUIncludeArgs(const ArgList &Args,
                                         ArgStringList &CC1Args) const {
   HostTC.AddIAMCUIncludeArgs(Args, CC1Args);
 }
 
 SanitizerMask CudaToolChain::getSupportedSanitizers() const {
-  // The CudaToolChain only supports address sanitization in the sense that it
-  // allows ASAN arguments on the command line. It must not error out on these
-  // command line arguments because the host code compilation supports them.
-  // However, it doesn't actually do any address sanitization for device code;
-  // instead, it just ignores any ASAN command line arguments it sees.
-  return SanitizerKind::Address;
+  // The CudaToolChain only supports sanitizers in the sense that it allows
+  // sanitizer arguments on the command line if they are supported by the host
+  // toolchain. The CudaToolChain will actually ignore any command line
+  // arguments for any of these "supported" sanitizers. That means that no
+  // sanitization of device code is actually supported at this time.
+  //
+  // This behavior is necessary because the host and device toolchains
+  // invocations often share the command line, so the device toolchain must
+  // tolerate flags meant only for the host toolchain.
+  return HostTC.getSupportedSanitizers();
 }
 
 /// XCore tool chain
 XCoreToolChain::XCoreToolChain(const Driver &D, const llvm::Triple &Triple,
                                const ArgList &Args)
     : ToolChain(D, Triple, Args) {
   // ProgramPaths are found via 'PATH' environment variable.
 }