m4macros: update ax_gcc_func_attribute.m4 to serial 12
The serial 7 of m4macros/ax_gcc_func_attribute.m4 has an issue that when Wstrict-prototypes is used with gcc, the attribute detection always fails even if the attribute is actually supported. In such case the fish cache will never be constructed. It's fixed in serial 12 of the macro in autoconf-archive and this change updates the one distributed with GIMP to serial 12.
Showing with 18 additions and 2 deletions