LLLexer.h - reduce SourceMgr.h include to SMLoc.h. NFC

We only need the SMLoc definition and the SourceMgr forward declaration.

llvm/lib/AsmParser/LLLexer.h

@@ -16,12 +16,13 @@
 #include "LLToken.h"
 #include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/APSInt.h"
-#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/SMLoc.h"
 #include <string>
 
 namespace llvm {
   class Type;
   class SMDiagnostic;
+  class SourceMgr;
   class LLVMContext;
 
   class LLLexer {