[Driver] Allow drivers to add multiple libc++ include paths

This allows toolchain drivers to add multiple libc++ include paths akin
to libstdc++. This is useful in multiarch setup when some headers might
be in target specific include directory. There should be no functional
change.

Differential Revision: https://reviews.llvm.org/D45422

llvm-svn: 329748
diff --git a/clang/lib/Driver/ToolChains/Linux.h b/clang/lib/Driver/ToolChains/Linux.h
index 9778c18..22dbbec 100644
--- a/clang/lib/Driver/ToolChains/Linux.h
+++ b/clang/lib/Driver/ToolChains/Linux.h
@@ -27,7 +27,9 @@
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
-  std::string findLibCxxIncludePath() const override;
+  void addLibCxxIncludePaths(
+      const llvm::opt::ArgList &DriverArgs,
+      llvm::opt::ArgStringList &CC1Args) const override;
   void addLibStdCxxIncludePaths(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;