[driver] Revert r180652 and 180658 and temporarily #define MAXPATHLEN to
make the gdb tests and the Windows bots happy.

The Path::GetCurrentDirectory API is not equivalent to ::getcwd(), so 
r180652 causes a gdb tests to fail.  On the other hand, <sys/param.h> 
isn't defined on Windows systems, so that causes Windows builds to fail.
rdar://12237559

llvm-svn: 180661
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 5d152e5..40aebd4 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1775,6 +1775,9 @@
   return true;
 }
 
+// FIXME: This is a temporary hack until I can find a fix that works for all
+// platforms.
+#define MAXPATHLEN 4096
 /// If the PWD environment variable is set, add a CC1 option to specify the
 /// debug compilation directory.
 static void addDebugCompDirArg(const ArgList &Args, ArgStringList &CmdArgs) {
@@ -1792,8 +1795,8 @@
     return;
   }
   // Fall back to using getcwd.
-  std::string cwd = llvm::sys::Path::GetCurrentDirectory().str();
-  if (pwd && !cwd.empty()) {
+  char *cwd;
+  if (pwd && ::getcwd(cwd, MAXPATHLEN)) {
     CmdArgs.push_back("-fdebug-compilation-dir");
     CmdArgs.push_back(Args.MakeArgString(cwd));
   }