Does someone know a C compiler which does not rely on gcc? [closed]

I am trying to see if my code is portable among many compilers other than GCC and absolutely other than compiler that accept the GNU C dialects, because I am using a lot of extensions and attributes. For attributes I have used the operator _has_attribute to check if the attribute's features are implemented, but for extensions it is not so quite easy. So I need to do some test to the program's portability to see what I should modify. Does someone know a compiler which does not rely on gcc?