Unify thread pool logic across the rest of the compiler, using a global thread pool

src/parser.hpp

@@ -191,6 +191,7 @@ struct Parser {
 	isize                     file_to_process_count;
 	isize                     total_token_count;
 	isize                     total_line_count;
+	BlockingMutex             wait_mutex;
 	BlockingMutex             import_mutex;
 	BlockingMutex             file_add_mutex;
 	BlockingMutex             file_decl_mutex;
@@ -198,9 +199,6 @@ struct Parser {
 	MPMCQueue<ParseFileError> file_error_queue;
 };
 
-
-gb_global ThreadPool parser_thread_pool = {};
-
 struct ParserWorkerData {
 	Parser *parser;
 	ImportedFile imported_file;