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/BuildLibuv.cmake

@@ -45,11 +45,24 @@ if(UNIX)
     CONFIGURE_COMMAND ${UNIX_CFGCMD} MAKE=${MAKE_PRG}
     INSTALL_COMMAND ${MAKE_PRG} V=1 install)
 
+elseif(MINGW AND CMAKE_CROSSCOMPILING)
+  # Build libuv for the host
+  BuildLibuv(TARGET libuv_host
+    CONFIGURE_COMMAND sh ${DEPS_BUILD_DIR}/src/libuv_host/autogen.sh && ${DEPS_BUILD_DIR}/src/libuv_host/configure --with-pic --disable-shared --prefix=${HOSTDEPS_INSTALL_DIR} CC=${HOST_C_COMPILER}
+    INSTALL_COMMAND ${MAKE_PRG} V=1 install)
+
+  # Build libuv for the target
+  BuildLibuv(
+    CONFIGURE_COMMAND ${UNIX_CFGCMD} --host=${CROSS_TARGET}
+    INSTALL_COMMAND ${MAKE_PRG} V=1 install)
+
 elseif(WIN32)
 
   set(UV_OUTPUT_DIR ${DEPS_BUILD_DIR}/src/libuv/${CMAKE_BUILD_TYPE})
   if(MSVC)
     set(BUILD_SHARED ON)
+  elseif(MINGW)
+    set(BUILD_SHARED OFF)
   else()
     message(FATAL_ERROR "Trying to build libuv in an unsupported system ${CMAKE_SYSTEM_NAME}/${CMAKE_C_COMPILER_ID}")
   endif()