Do not enforce compilers / flags

--- jfaudiolib/Makefile.orig	2014-11-13 09:26:16.821946185 +0100
+++ jfaudiolib/Makefile	2014-11-13 09:42:05.999047069 +0100
@@ -8,9 +8,9 @@
  OPTLEVEL=-O2
 endif
 
-CC=gcc
-CFLAGS=-g $(OPTLEVEL) -Wall
-CPPFLAGS=-Iinclude -Isrc
+CC?=gcc
+CFLAGS+=-Wall
+CPPFLAGS+=-Iinclude -Isrc
 
 SOURCES=src/drivers.c \
         src/fx_man.c \