gollvm: add /usr/ to toolchain paths for Redhat

Change-Id: I79f32c5e448d435efd2da9d92fc0dcd1d5aeca91
Reviewed-on: https://go-review.googlesource.com/c/gollvm/+/406115
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
diff --git a/driver/LinuxToolChain.cpp b/driver/LinuxToolChain.cpp
index 73037f1..2a2fb10 100644
--- a/driver/LinuxToolChain.cpp
+++ b/driver/LinuxToolChain.cpp
@@ -73,7 +73,7 @@
                                       "/../" + ftrip).str());
   addIfPathExists(fpaths, llvm::Twine(osLibDir).str());
   addIfPathExists(fpaths, llvm::Twine(osLibDir + "/" + ftrip).str());
-  if (this->distro_ == distro::DistroArchLinux)
+  if (this->distro_ == distro::DistroArchLinux || this->distro_ == distro::DistroRedhat)
     addIfPathExists(fpaths, llvm::Twine("/usr/" + osLibDir).str());
 
   // Include program and file paths in verbose output.