Minor fix in ToolChainTest.cpp to allow user defined GCC toolchain.

[sfantao]

Summary

If the user configured clang with a custom GCC toolchain that will take precedence on what the ToolChainTest.cpp expects to evaluate. This was causing the test to fail in these cases.

This patch fixes the issue by passing --gcc-toolchain= to the driver, in order to override any user defined GCC toolchain.

[bkramer]

This should be fine. Sorry for the breakage.

[sfantao]

Committed in r251459.

Thanks!
Samuel

unittests/Driver/ToolChainTest.cpp

const char *EmptyFiles[] = {
       "/usr/include/arm-linux-gnueabihf/.keep",
       "/lib/arm-linux-gnueabi/.keep",
       "/lib/arm-linux-gnueabihf/.keep"};
 
   for (const char *Path : EmptyFiles)
     InMemoryFileSystem->addFile(Path, 0,
                                 llvm::MemoryBuffer::getMemBuffer("\n"));
 
-  std::unique_ptr<Compilation> C(
-      TheDriver.BuildCompilation({"-fsyntax-only", "foo.cpp"}));
+  std::unique_ptr<Compilation> C(TheDriver.BuildCompilation(
+      {"-fsyntax-only", "--gcc-toolchain=", "foo.cpp"}));
 
   std::string S;
   {
     llvm::raw_string_ostream OS(S);
     C->getDefaultToolChain().printVerboseInfo(OS);
   }
 #if LLVM_ON_WIN32
   std::replace(S.begin(), S.end(), '\\', '/');
TEST(ToolChainTest, VFSGCCInstallationRelativeDir) {
   const char *EmptyFiles[] = {
       "foo.cpp", "/home/test/lib/gcc/arm-linux-gnueabi/4.6.1/crtbegin.o",
       "/home/test/include/arm-linux-gnueabi/.keep"};
 
   for (const char *Path : EmptyFiles)
     InMemoryFileSystem->addFile(Path, 0,
                                 llvm::MemoryBuffer::getMemBuffer("\n"));
 
-  std::unique_ptr<Compilation> C(
-      TheDriver.BuildCompilation({"-fsyntax-only", "foo.cpp"}));
+  std::unique_ptr<Compilation> C(TheDriver.BuildCompilation(
+      {"-fsyntax-only", "--gcc-toolchain=", "foo.cpp"}));
 
   std::string S;
   {
     llvm::raw_string_ostream OS(S);
     C->getDefaultToolChain().printVerboseInfo(OS);
   }
 #if LLVM_ON_WIN32
   std::replace(S.begin(), S.end(), '\\', '/');