Mark checkSignature const, and in turn stop casting away const from
ArchiveMemberHeader. Found by gcc48 -Wcast-qual.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163255 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Archive/ArchiveInternals.h b/lib/Archive/ArchiveInternals.h
index 55684f7..639f5ac 100644
--- a/lib/Archive/ArchiveInternals.h
+++ b/lib/Archive/ArchiveInternals.h
@@ -66,7 +66,7 @@
       fmag[1] = '\n';
     }
 
-    bool checkSignature() {
+    bool checkSignature() const {
       return 0 == memcmp(fmag, ARFILE_MEMBER_MAGIC,2);
     }
   };