[Bug bootstrap/115416] [13/14/15 regression] Setting --includedir to a nonexistent directory causes a build error since r13-5490-g59e4c98173a79f

["marcuscalhounlopez at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115416

--- Comment #5 from Marcus Calhoun-Lopez <marcuscalhounlopez at gmail dot com> ---
(In reply to YunQiang Su from comment #3)
> Since it doesn't exist, why use --includedir with it?

/opt/local/include/gcc is where the header files will be installed after the
build, so there is no reason for it to exist before the build.

> Anyway, so, maybe we should detect the existence of this dir.
> Can you have a try of this patch?
> 
> --- a/gcc/Makefile.in
> +++ b/gcc/Makefile.in
> @@ -560,10 +560,11 @@ LINKER_PLUGIN_API_H = $(srcdir)/../include/plugin-api.h
>  # Default native SYSTEM_HEADER_DIR, to be overridden by targets.
>  NATIVE_SYSTEM_HEADER_DIR = @NATIVE_SYSTEM_HEADER_DIR@
>  # Default cross SYSTEM_HEADER_DIR, to be overridden by targets.
> -ifeq (@includedir@,$(prefix)/include)
> -  CROSS_SYSTEM_HEADER_DIR = @CROSS_SYSTEM_HEADER_DIR@
> -else
> -  CROSS_SYSTEM_HEADER_DIR = @includedir@
> +CROSS_SYSTEM_HEADER_DIR = @CROSS_SYSTEM_HEADER_DIR@
> +ifneq (@includedir@,$(prefix)/include)
> +  ifneq (,$(wildcard @includedir@))
> +    CROSS_SYSTEM_HEADER_DIR = @includedir@
> +  endif
>  endif

Yes, this seems to work.
Thank you very much.