$NetBSD$

Allow pkgsrc to set CC

--- makefile.cvc64.orig	2023-07-16 21:42:51.000000000 +0000
+++ makefile.cvc64
@@ -115,7 +115,7 @@ CFLAGS= $(ARCHFLGS) -pipe $(WARNS) $(INC
 # CFLAGS= $(ARCHFLGS) -pipe $(WARNS) $(INCS) -D__DBMALLOC__ $(CVCCFLGS) -g 
 
 # select gcc version to use - for older Linux systems may need older compiler
-CC=gcc
+CC?=gcc
 
 # this is ld equivalent of gcc -m32 so not used here
 # LD=ld -m elf_i386