ac: use LLVMContextSetOpaquePointers if available

Disabling opaque pointers in LLVM doesn't fix all the issues but
it makes pointers non-opaque by default (eg LLVMPointerType()
returns a typed pointer).

Reviewed-by: Mihai Preda <mhpreda@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17361>

src/amd/llvm/ac_llvm_build.c

@@ -62,6 +62,9 @@ void ac_llvm_context_init(struct ac_llvm_context *ctx, struct ac_llvm_compiler *
                           unsigned ballot_mask_bits)
 {
    ctx->context = LLVMContextCreate();
+   #if LLVM_VERSION_MAJOR >= 15
+   LLVMContextSetOpaquePointers(ctx->context, false);
+   #endif
 
    ctx->gfx_level = gfx_level;
    ctx->family = family;