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/compiler/meson.build

@@ -97,5 +97,8 @@ if with_tests
   )
 endif
 
+if with_clc
+  subdir('clc')
+endif
 subdir('glsl')
 subdir('isaspec')