Add string_set.cpp; Code clean up

src/check_stmt.cpp

@@ -1670,7 +1670,7 @@ void check_stmt_internal(Checker *c, AstNode *node, u32 flags) {
 		CheckerContext prev_context = c->context;
 		if (ok) {
 			c->context.curr_foreign_library = foreign_library;
-			c->context.default_foreign_cc = ProcCC_C;
+			c->context.default_foreign_cc = ProcCC_CDecl;
 		}
 
 		check_foreign_block_decl_attributes(c, fb);