revert: "ci: remove mingw job #18580"

This partially reverts commit f8af81445b.

The mingw parts of cmake was removed to see if it was still used
(ref: https://github.com/neovim/neovim/pull/18580). It turns out it is,
so this will fix that.

Closes: https://github.com/neovim/neovim/issues/18597

third-party/cmake/BuildLuarocks.cmake

@@ -56,7 +56,7 @@ endif()
 # Defaults to 5.1 for bundled LuaJIT/Lua.
 set(LUA_VERSION "5.1")
 
-if(UNIX)
+if(UNIX OR (MINGW AND CMAKE_CROSSCOMPILING))
 
   if(USE_BUNDLED_LUAJIT)
     list(APPEND LUAROCKS_OPTS
@@ -94,9 +94,13 @@ if(UNIX)
     CONFIGURE_COMMAND ${DEPS_BUILD_DIR}/src/luarocks/configure
       --prefix=${HOSTDEPS_INSTALL_DIR} --force-config ${LUAROCKS_OPTS}
     INSTALL_COMMAND ${MAKE_PRG} -j1 bootstrap)
-elseif(MSVC)
+elseif(MSVC OR MINGW)
 
-  set(COMPILER_FLAG /MSVC)
+  if(MINGW)
+    set(COMPILER_FLAG /MW)
+  elseif(MSVC)
+    set(COMPILER_FLAG /MSVC)
+  endif()
 
   # Ignore USE_BUNDLED_LUAJIT - always ON for native Win32
   BuildLuarocks(INSTALL_COMMAND install.bat /FORCECONFIG /NOREG /NOADMIN /Q /F
@@ -119,6 +123,9 @@ list(APPEND THIRD_PARTY_DEPS luarocks)
 
 if(USE_BUNDLED_LUAJIT)
   add_dependencies(luarocks luajit)
+  if(MINGW AND CMAKE_CROSSCOMPILING)
+    add_dependencies(luarocks luajit_host)
+  endif()
 elseif(USE_BUNDLED_LUA)
   add_dependencies(luarocks lua)
 endif()
@@ -189,6 +196,9 @@ if(USE_BUNDLED_BUSTED)
   set(LUV_DEPS luacheck)
   if(USE_BUNDLED_LUV)
     list(APPEND LUV_DEPS luv-static lua-compat-5.3)
+    if(MINGW AND CMAKE_CROSSCOMPILING)
+      list(APPEND LUV_DEPS libuv_host)
+    endif()
     set(LUV_ARGS "CFLAGS=-O0 -g3 -fPIC")
     if(USE_BUNDLED_LIBUV)
       list(APPEND LUV_ARGS LIBUV_DIR=${HOSTDEPS_INSTALL_DIR})