Constify the argument to SourceLocation::getFromPtrEncoding.

This allows SourceLocations to be stored in generic "data" fields
that are typed as "const void *" and are also used to point to
const objects.

Really we should probably be returning a const pointer from
getPtrEncoding as well, but in some places we want to store
SourceLocations in the same generic "data" field as proper
pointers to /mutable/ objects. Oh well.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159868 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang/Basic/SourceLocation.h b/include/clang/Basic/SourceLocation.h
index 3bac26f..d6bba38 100644
--- a/include/clang/Basic/SourceLocation.h
+++ b/include/clang/Basic/SourceLocation.h
@@ -166,7 +166,7 @@
 
   /// getFromPtrEncoding - Turn a pointer encoding of a SourceLocation object
   /// into a real SourceLocation.
-  static SourceLocation getFromPtrEncoding(void *Encoding) {
+  static SourceLocation getFromPtrEncoding(const void *Encoding) {
     return getFromRawEncoding((unsigned)(uintptr_t)Encoding);
   }