[NFC] Header cleanup

Removed some unused headers, replaced some headers with forward class declarations.

Found using simple scripts like this one:
clear && ack --cpp -l '#include "llvm/ADT/IndexedMap.h"' | xargs grep -L 'IndexedMap[<]' | xargs grep -n --color=auto 'IndexedMap'

Patch by Eugene Kosov <claprix@yandex.ru>

Differential Revision: http://reviews.llvm.org/D19219

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 266595

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/tools/opt/NewPMDriver.h b/llvm/tools/opt/NewPMDriver.h
index 349a7b1267f..66a470d49ba 100644
--- a/llvm/tools/opt/NewPMDriver.h
+++ b/llvm/tools/opt/NewPMDriver.h
@@ -21,9 +21,8 @@
 #ifndef LLVM_TOOLS_OPT_NEWPMDRIVER_H
 #define LLVM_TOOLS_OPT_NEWPMDRIVER_H
 
-#include "llvm/ADT/StringRef.h"
-
 namespace llvm {
+class StringRef;
 class LLVMContext;
 class Module;
 class TargetMachine;