zsnes: fix the build against gcc-15

Without the change the build fails on `master` at `x86_640linux` as:

    chips/dsp3emu.c:31:23: error: 'bool' cannot be defined via 'typedef'
      31 | typedef unsigned char bool;
         |                       ^~~~

pkgs/applications/emulators/zsnes/default.nix

@@ -60,7 +60,8 @@ stdenv.mkDerivation {
   # Workaround build failure on -fno-common toolchains:
   #   ld: initc.o:(.bss+0x28): multiple definition of `HacksDisable'; cfg.o:(.bss+0x59e3): first defined here
   # Use pre-c++17 standard (c++17 forbids throw annotations)
-  env.NIX_CFLAGS_COMPILE = "-fcommon -std=c++14";
+  # Use pre-c23: chips/dsp3emu.c:31:23: error: 'bool' cannot be defined via 'typedef'
+  env.NIX_CFLAGS_COMPILE = "-fcommon -std=c++14 -std=gnu17";
 
   preConfigure = ''
     cd src