Take DW_AT_comp_dir from $PWD when it's present and starts with a '/'. This is
closer to what GCC does, except that GCC also checks that the inodes for $PWD
and '.' match.

llvm-svn: 142633
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 2dcb61b..ad32bc7 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1625,6 +1625,16 @@
   if (ShouldDisableDwarfDirectory(Args, getToolChain()))
     CmdArgs.push_back("-fno-dwarf-directory-asm");
 
+  if (const char *pwd = ::getenv("PWD")) {
+    // GCC also verifies that stat(pwd) and stat(".") have the same inode
+    // number. Not doing those because stats are slow, but we could.
+    if (pwd[0] == '/') {
+      std::string CompDir = pwd;
+      CmdArgs.push_back("-fdebug-compilation-dir");
+      CmdArgs.push_back(Args.MakeArgString(CompDir));
+    }
+  }
+
   if (Arg *A = Args.getLastArg(options::OPT_ftemplate_depth_)) {
     CmdArgs.push_back("-ftemplate-depth");
     CmdArgs.push_back(A->getValue(Args));