diff -up gsm-1.0-pl18/Makefile.orig gsm-1.0-pl18/Makefile
--- gsm-1.0-pl18/Makefile.orig	2023-04-14 22:20:16.910186912 +0800
+++ gsm-1.0-pl18/Makefile	2023-04-14 22:25:09.582803780 +0800
@@ -43,7 +43,8 @@ WAV49	= -DWAV49
 # CC		= /usr/lang/acc
 # CCFLAGS 	= -c -O
 
-CC		= gcc -ansi -pedantic
+CC		?= gcc
+CC		:= $(CC) -ansi -pedantic
 CCFLAGS 	= -c $(RPM_OPT_FLAGS) -DNeedFunctionPrototypes=1 -Wall -Wno-comment -D_XOPEN_SOURCE=700 -D_REENTRANT -fPIC
 
 LD 		= $(CC)