Fix Windows cross-compile issue after curl upgrade

Without include directories in RCFLAGS, libcurl.rc couldn't find
its #include <winver.h>.

tools/windows-cross/toolchain.cmake

@@ -7,6 +7,7 @@ set(CMAKE_C_COMPILER_TARGET i686-pc-windows-msvc)
 set(CMAKE_CXX_COMPILER_TARGET ${CMAKE_C_COMPILER_TARGET})
 set(CMAKE_C_FLAGS_INIT "-fms-compatibility /imsvc/xwin/crt/include /imsvc/xwin/sdk/include/ucrt /imsvc/xwin/sdk/include/um /imsvc/xwin/sdk/include/shared")
 set(CMAKE_CXX_FLAGS_INIT ${CMAKE_C_FLAGS_INIT})
+set(CMAKE_RC_FLAGS_INIT ${CMAKE_C_FLAGS_INIT})
 set(CMAKE_LINKER lld-link)
 set(CMAKE_MT llvm-mt)  # CMake can find rc=llvm-rc all by itself, but needs to be told mt=llvm-mt
 set(CMAKE_EXE_LINKER_FLAGS_INIT "/LIBPATH:/xwin/crt/lib/x86 /LIBPATH:/xwin/sdk/lib/um/x86 /LIBPATH:/xwin/sdk/lib/ucrt/x86")