[CMAKE] Fix compiling 32-bit targets on 64-bit clang-cl

With help of @tkreuzer and @julenuri I got x86_64-pc-windows-msvc flavor
of LLVM 13.0.1 compiling 32-bit ReactOS.

Author: SigmaTel71

toolchain-msvc.cmake

@@ -43,6 +43,11 @@ if(USE_CLANG_CL)
         set(CMAKE_CXX_COMPILER_TARGET "i686-pc-windows-msvc")
     endif()
 
+    if (ARCH STREQUAL "arm" OR ARCH STREQUAL "i386")
+        set(CMAKE_C_FLAGS "-m32")
+        set(CMAKE_CXX_FLAGS "-m32")
+    endif()
+
     # Avoid wrapping RC compiler with cmcldeps utility for clang-cl.
     # Otherwise it breaks cross-compilation (32bit ReactOS cannot be compiled by 64bit LLVM),
     # target architecture is not passed properly