libgcc: build arm-{isa,cpu}.h for all 32-bit arm, not just armv7

As reported here:

https://github.com/NixOS/nixpkgs/pull/247900#issuecomment-1679258061

pkgs/development/libraries/gcc/libgcc/default.nix

···
         insn-constants.h \
   '' + lib.optionalString stdenv.targetPlatform.isM68k ''
         sysroot-suffix.h \
-  '' + lib.optionalString stdenv.targetPlatform.isArmv7 ''
+  '' + lib.optionalString stdenv.targetPlatform.isAarch32 ''
         arm-isa.h \
         arm-cpu.h \
   '' + ''