use the system libgsm if available (issue #5434, modified to still work with builtin libgsm)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@7539 65c4cc65-6c06-0410-ace0-fbb531ad65f3

codecs/Makefile

@@ -60,8 +60,18 @@ ifneq ($(wildcard ilbc/iLBC_decode.h),)
 endif
 
 
+LIBGSM_PATH:=/usr/local/include /usr/include
+LIBGSM_SYSTEM_HEADERS:=$(wildcard $(LIBGSM_PATH:%=$(CROSS_COMPILE_TARGET)%/gsm/gsm.h))
+ifneq (,$(LIBGSM_SYSTEM_HEADERS))
+LIBGSM=-lgsm
+LIBGSMT=
+CFLAGS+=-DUSE_EXTERNAL_GSM_LIB
+else
 LIBGSM=gsm/lib/libgsm.a
-LIBGSMT=gsm/lib/libgsm.a
+LIBGSMT=$(LIBGSM)
+CFLAGS+=-I.
+endif
+
 LIBLPC10=lpc10/liblpc10.a
 
 ifeq ($(findstring BSD,${OSARCH}),BSD)

codecs/codec_gsm.c

@@ -45,7 +45,12 @@ ASTERISK_FILE_VERSION(__FILE__, "$Revision$")
 #include "asterisk/logger.h"
 #include "asterisk/channel.h"
 
+#ifdef USE_EXTERNAL_GSM_LIB
+#include <gsm/gsm.h>
+#else
 #include "gsm/inc/gsm.h"
+#endif
+
 #include "../formats/msgsm.h"
 
 /* Sample frame data */