bug#11207: configure: new option --enable-gcc-warnings

[Glenn Morris]

Paul Eggert wrote:

> --- src/regex.c       2012-01-19 07:21:25 +0000
> +++ src/regex.c       2012-04-09 07:45:59 +0000
> @@ -33,6 +33,19 @@
>    #pragma alloca
>  #endif
>  
> +/* Ignore some GCC warnings for now.  This section should go away
> +   once the Emacs and Gnulib regex code is merged.  */
> +#if (__GNUC__ == 4 && 3 <= __GNUC_MINOR__) || 4 < __GNUC__
> +# pragma GCC diagnostic ignored "-Wstrict-overflow"
> +# ifndef emacs
> +#  pragma GCC diagnostic ignored "-Wunused-but-set-variable"
> +#  pragma GCC diagnostic ignored "-Wunused-function"
> +#  pragma GCC diagnostic ignored "-Wunused-macros"
> +#  pragma GCC diagnostic ignored "-Wunused-result"
> +#  pragma GCC diagnostic ignored "-Wunused-variable"
> +# endif
> +#endif

For me on RHEL6, using gcc 4.4.6 20110731 (Red Hat 4.4.6-3), the
"-Wunused-result" line causes a gripe when building lib-src/regex.o:

src/regex.c:44: warning: unknown option after '#pragma GCC diagnostic' kind