Fix build with GCC:
 - GCC doesn't support #pragma mark, only Apple GCC and clang. Wrap the pragma mark's in #if 0 to make gcc ignore them but xcode still see them.
 - Wrap a bunch of "#pragma clang" lines in #ifdef __clang__.
 - Pacify gcc's -Wparenthesis in a case where it's quite reasonable.


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@231344 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/cxa_demangle.cpp b/src/cxa_demangle.cpp
index 2d07686..1344f43 100644
--- a/src/cxa_demangle.cpp
+++ b/src/cxa_demangle.cpp
@@ -4711,7 +4711,7 @@
 
     std::size_t 
     align_up(std::size_t n) noexcept
-        {return n + (alignment-1) & ~(alignment-1);}
+        {return (n + (alignment-1)) & ~(alignment-1);}
 
     bool
     pointer_in_buffer(char* p) noexcept