Move a bunch of the CLC stuff from src/microsoft to common code

The D3D12-specific stuff isn't useful to have in common code but all the
stuff to invoke clang really should be common.

v2: Rebase (Lionel)

v3: Define a new clc_libclc_new_dxil() entrypoint to create a clc
    context with DXIL nir_options (Jesse)

v4: Fixup meson build (Lionel)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9156>

src/microsoft/clc/compute_test.cpp

@@ -622,10 +622,10 @@ ComputeTest::SetUp()
    static struct clc_libclc *compiler_ctx_g = nullptr;
 
    if (!compiler_ctx_g) {
-      clc_libclc_options options = { };
+      clc_libclc_dxil_options options = { };
       options.optimize = (debug_get_option_debug_compute() & COMPUTE_DEBUG_OPTIMIZE_LIBCLC) != 0;
 
-      compiler_ctx_g = clc_libclc_new(&logger, &options);
+      compiler_ctx_g = clc_libclc_new_dxil(&logger, &options);
       if (!compiler_ctx_g)
          throw runtime_error("failed to create CLC compiler context");