lua5_1: fixup a recent regression

Commit 57832e625c (PR #119860) switched to using SYSCFLAGS,
but lua 5.1 calls it MYCFLAGS. We noticed due to broken luarocks build:
https://hydra.nixos.org/build/142663274

Changed files
+2 -1
pkgs
development
interpreters
+2 -1
pkgs/development/interpreters/lua-5/interpreter.nix
···
configurePhase = ''
runHook preConfigure
-
makeFlagsArray+=(CFLAGS='-O2 -fPIC${lib.optionalString compat " -DLUA_COMPAT_ALL"} $(SYSCFLAGS)' )
+
makeFlagsArray+=(CFLAGS='-O2 -fPIC${lib.optionalString compat " -DLUA_COMPAT_ALL"} $(${
+
if lib.versionAtLeast luaversion "5.2" then "SYSCFLAGS" else "MYCFLAGS"})' )
makeFlagsArray+=(${lib.optionalString stdenv.isDarwin "CC=\"$CC\""}${lib.optionalString (stdenv.buildPlatform != stdenv.hostPlatform) " 'AR=${stdenv.cc.targetPrefix}ar rcu'"})
installFlagsArray=( TO_BIN="lua luac" INSTALL_DATA='cp -d' \