Fix -Wunused-comparison for comparisons in arguments to function-like macros.

Previously, -Wunused-comparison ignored comparisons in both macro bodies and
macro arguments, but we would still emit a -Wunused-value warning for either.
Now we correctly emit -Wunused-comparison for expressions in macro arguments.

Also, add isMacroBodyExpansion to SourceManager, to go along with
isMacroArgExpansion.

llvm-svn: 172279
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index b738793..a9d3dd5 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -126,7 +126,7 @@
 
   // Suppress warnings when the operator, suspicious as it may be, comes from
   // a macro expansion.
-  if (Loc.isMacroID())
+  if (S.SourceMgr.isMacroBodyExpansion(Loc))
     return false;
 
   S.Diag(Loc, diag::warn_unused_comparison)