Clang does not support -fthread-jumps as of now.
This fixes "cc: error: unknown argument: '-fthread-jumps'"

Replace hardcoded "gcc" with $CC

Include system $CFLAGS to the local CFLAGS variable

--- Makefile.orig	2025-04-05 22:56:41 UTC
+++ Makefile
@@ -50,14 +50,13 @@ ifeq ($(origin CC),default)
 ######################################################################
 
 ifeq ($(origin CC),default)
-CC = gcc
+CC = ${CC}
 endif
 
 PKG_CONFIG ?= pkg-config
 INSTALL    ?= install
-CFLAGS    = -O2 -Wall \
-	    -fcaller-saves -ffast-math -fno-strength-reduce \
-	    -fthread-jumps
+CFLAGS    := ${CFLAGS} -Wall \
+	    -fcaller-saves -ffast-math -fno-strength-reduce
 
 GDK_VERS := 3