meson: Error if LLVM is turned off but clover it turned on

Since clover has a hard requirement on LLVM

v2: - make error message more specific

Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
diff --git a/meson.build b/meson.build
index 4654125..917186a 100644
--- a/meson.build
+++ b/meson.build
@@ -1260,6 +1260,8 @@
   endif
 elif with_amd_vk or with_gallium_radeonsi or with_gallium_swr
   error('The following drivers require LLVM: Radv, RadeonSI, SWR. One of these is enabled, but LLVM is disabled.')
+elif with_gallium_opencl
+  error('The OpenCL "Clover" state tracker requires LLVM, but LLVM is disabled.')
 endif
 
 if (with_amd_vk or with_gallium_radeonsi or with_gallium_opencl or