[Driver] Search compiler-rt paths in -print-file-name=

This makes it possible to print the name of compiler-rt libraries
by using simply clang -print-file-name=libclang_rt.${runtime}-${arch}.so
same as other libraries, without having to know the details of the
resource directory organization.

Differential Revision: https://reviews.llvm.org/D35820

llvm-svn: 310548
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index e1c6325..b11629a 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -3682,7 +3682,12 @@
       return P.str();
   }
 
-  SmallString<128> P(ResourceDir);
+  SmallString<128> R(ResourceDir);
+  llvm::sys::path::append(R, Name);
+  if (llvm::sys::fs::exists(Twine(R)))
+    return R.str();
+
+  SmallString<128> P(TC.getCompilerRTPath());
   llvm::sys::path::append(P, Name);
   if (llvm::sys::fs::exists(Twine(P)))
     return P.str();