Consolidate the existing checks for __APPLE__ and __clang__ into one,
but only use it as long as __GNUC__ is defined (clang operating in
gcc compatible mode, as opposed to MSVC compatible mode) and as
long as __SEH__ isn't defined (which it is while cross compiling
targeting windows, when SEH is used as unwind format).
Signed-off-by: Martin Storsjo <martin@martin.st>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>