we are targeting GNU extensions, GNU attributes are a part of that.
added aliases for the new attribute names (name as all caps = shorter
due to `atrb_` prefix)
The aliases are likely to be removed in a later commit
I am choosing gnu99 over c99, since I am planning to use GNU extensions,
like bswap. (in a future commit)
Why I choose c99 over c17, is because this'll produce more portable
code.
c99 does not implement noreturn.h, thus I added it to the compiler
attributes header.