Move compiler.h and imports.h/c from src/mesa/main into src/util

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4324>
diff --git a/src/meson.build b/src/meson.build
index 53b999a..accb7a9 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -31,7 +31,7 @@
 libglsl_util = static_library(
   'glsl_util',
   files(
-    'mesa/main/extensions_table.c', 'mesa/main/imports.c',
+    'mesa/main/extensions_table.c',
     'mesa/program/prog_parameter.c', 'mesa/program/symbol_table.c',
     'mesa/program/dummy_errors.c',
   ),