vulkan: Improve build time for MSVC (#16545)

Enable CMP0147 so custom build steps (invoking vulkan-shader-gen) are run in parallel.

Enable /MP so source files are compiled in parallel.

ggml/src/ggml-vulkan/CMakeLists.txt

@@ -1,9 +1,18 @@
 cmake_minimum_required(VERSION 3.19)
 cmake_policy(SET CMP0114 NEW)
 cmake_policy(SET CMP0116 NEW)
+if (POLICY CMP0147)
+    # Parallel build custom build steps
+    cmake_policy(SET CMP0147 NEW)
+endif()
 
 find_package(Vulkan COMPONENTS glslc REQUIRED)
 
+if (CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+    # Parallel build object files
+    add_definitions(/MP)
+endif()
+
 function(detect_host_compiler)
     if (CMAKE_HOST_SYSTEM_NAME STREQUAL "Windows")
         find_program(HOST_C_COMPILER NAMES cl gcc clang NO_CMAKE_FIND_ROOT_PATH)