Refactor to remove un-named struct gnu extension usage. Now ISO C89 and C99 compliant. Comment trailing endifs

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@78537 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/ffsti2.c b/lib/ffsti2.c
index 2ee1a8b..668b542 100644
--- a/lib/ffsti2.c
+++ b/lib/ffsti2.c
@@ -34,4 +34,4 @@
     return __builtin_ctzll(x.low) + 1;
 }
 
-#endif
+#endif /* __x86_64 */