add several __has_something macro

With these macros implemented we can write codes just like we can assume
the compiler being clang.  MSC_VERSION_SINCE is defined to implement
those macros, but turned out to be handy for other places.  The -fdeclspec
compiler flag is necessary for clang to properly handle __has_declspec().

1 files changed, 0 insertions, 2 deletions

diff --git a/internal/gc.h b/internal/gc.h
index cf59eaed0b..6e3fb8996d 100644
--- a/internal/gc.h
+++ b/internal/gc.h
@@ -47,11 +47,9 @@ RUBY_SYMBOL_EXPORT_END
                         rb_wb_unprotected_newobj_of(klass, flags))
 #define NEWOBJ_OF(obj,type,klass,flags) RB_NEWOBJ_OF(obj,type,klass,flags)
 
-#ifdef __has_attribute
 #if __has_attribute(alloc_align)
 __attribute__((__alloc_align__(1)))
 #endif
-#endif
 void *rb_aligned_malloc(size_t, size_t) RUBY_ATTR_MALLOC RUBY_ATTR_ALLOC_SIZE((2));
 
 size_t rb_size_mul_or_raise(size_t, size_t, VALUE); /* used in compile.c */