remove no longer needed gcc8 workaround. add gcc9 workaround
remove no longer needed gcc8 workaround. add gcc9 workaround

Occasionally LLVM headers generate warnings with newer gcc versions and
since we use -Werror this has to be worked around.

raulgrell/zig,zig-lang/zig,andrewrk/zig,andrewrk/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig