[clang] - Simplify tools::SplitDebugName.

This should be NFC change.

SplitDebugName recently started to accept the `Output` that
can be used to simplify the logic a bit, also it
seems that code in SplitDebugName that uses
OPT_fdebug_compilation_dir is simply dead.

Differential revision: https://reviews.llvm.org/D54576

llvm-svn: 347035
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index d7797d9..1af9935 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -817,7 +817,7 @@
   if (Args.hasArg(options::OPT_gsplit_dwarf) &&
       getToolChain().getTriple().isOSLinux())
     SplitDebugInfo(getToolChain(), C, *this, JA, Args, Output,
-                   SplitDebugName(Args, Inputs[0], Output));
+                   SplitDebugName(Args, Output));
 }
 
 namespace {