bug#57015: 29.0.50; macOS: libgccjit was not found: Homebrew libgccjit 12.1.0

[Eli Zaretskii]

> From: Naofumi Yasufuku <naofumi@yasufuku.dev>
> Cc: 57015@debbugs.gnu.org
> Date: Sun, 07 Aug 2022 01:36:39 +0900
> 
> --- a/configure.ac
> +++ b/configure.ac
> @@ -3843,8 +3843,15 @@ AC_DEFUN
>          if test -n "`$BREW --prefix --installed libgccjit 2>/dev/null`"; then
>            MAC_CFLAGS="-I$(dirname $($BREW ls -v libgccjit | \
>                                                  grep libgccjit.h))"
> -          MAC_LIBS="-L$(dirname $($BREW ls -v libgccjit| \
> -                                            grep -E 
> 'libgccjit\.(so|dylib)$'))"
> +          MAC_LIBS="-L$(dirname $($BREW ls -v libgccjit | \
> +                                  grep -E 'current/libgccjit\.(so|dylib)$' | 
> \
> +                                  head -1))"
> +          if test "x${MAC_LIBS}" = "x-L"; then
> +            # Try for Homebrew libgccjit < 12.1.0.
> +            MAC_LIBS="-L$(dirname $($BREW ls -v libgccjit | \
> +                                    grep -E 'libgccjit\.(so|dylib)$' | \
> +                                    head -1))"
> +          fi
>          fi
>        fi
>  

Is 'dirname' guaranteed to be available?