[OpenMP] Fix library path missing when using OpenMP

The changes in D122444 caused OpenMP programs built with the
LLVM_ENABLE_RUNTIMES options to stop finding the libraries. We generally
expect to link against the libraries associated with the clang
installation itself but we no longer implicitly included that directory.
This patch adds in the include path of the clang installations library
to ensure we can find them.

Reviewed By: jdoerfert, MaskRay

Differential Revision: https://reviews.llvm.org/D122592

(cherry picked from commit fceea4e)

Author: jhuber6

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -661,6 +661,17 @@ void tools::addOpenMPRuntimeSpecificRPath(const ToolChain &TC,
   }
 }
 
+void tools::addOpenMPRuntimeLibraryPath(const ToolChain &TC,
+                                        const ArgList &Args,
+                                        ArgStringList &CmdArgs) {
+  // Default to clang lib / lib64 folder, i.e. the same location as device
+  // runtime.
+  SmallString<256> DefaultLibPath =
+      llvm::sys::path::parent_path(TC.getDriver().Dir);
+  llvm::sys::path::append(DefaultLibPath, Twine("lib") + CLANG_LIBDIR_SUFFIX);
+  CmdArgs.push_back(Args.MakeArgString("-L" + DefaultLibPath));
+}
+
 void tools::addArchSpecificRPath(const ToolChain &TC, const ArgList &Args,
                                  ArgStringList &CmdArgs) {
   // Enable -frtlib-add-rpath by default for the case of VE.
@@ -720,6 +731,7 @@ bool tools::addOpenMPRuntime(ArgStringList &CmdArgs, const ToolChain &TC,
 
   if (RTKind == Driver::OMPRT_OMP)
     addOpenMPRuntimeSpecificRPath(TC, Args, CmdArgs);
+  addOpenMPRuntimeLibraryPath(TC, Args, CmdArgs);
 
   return true;
 }

clang/lib/Driver/ToolChains/CommonArgs.h

@@ -111,6 +111,9 @@ void addOpenMPRuntimeSpecificRPath(const ToolChain &TC,
                                    llvm::opt::ArgStringList &CmdArgs);
 void addArchSpecificRPath(const ToolChain &TC, const llvm::opt::ArgList &Args,
                           llvm::opt::ArgStringList &CmdArgs);
+void addOpenMPRuntimeLibraryPath(const ToolChain &TC,
+                                 const llvm::opt::ArgList &Args,
+                                 llvm::opt::ArgStringList &CmdArgs);
 /// Returns true, if an OpenMP runtime has been added.
 bool addOpenMPRuntime(llvm::opt::ArgStringList &CmdArgs, const ToolChain &TC,
                       const llvm::opt::ArgList &Args,

clang/test/Driver/openmp-library-path.c

@@ -0,0 +1,5 @@
+// RUN: %clang -### -fopenmp=libomp --target=x86_64-linux-gnu -ccc-install-dir %S/Inputs/basic_linux_tree/usr/bin %s 2>&1 | FileCheck %s
+
+void foo() {}
+
+// CHECK: -L{{.*}}Inputs{{.*}}basic_linux_tree