ftmod_misdn: Change last commit to set -D_GNU_SOURCE instead.

This fixes all build errors.
(Stand-alone build of FreeTDM worked fine, for some
 i-don't-really-want-to-know strange reason).
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

libs/freetdm/Makefile.am

@@ -251,7 +251,7 @@ endif
 if HAVE_MISDN
 mod_LTLIBRARIES += ftmod_misdn.la
 ftmod_misdn_la_SOURCES  = $(SRC)/ftmod/ftmod_misdn/ftmod_misdn.c
-ftmod_misdn_la_CFLAGS   = $(FTDM_CFLAGS) $(AM_CFLAGS) $(MISDN_CFLAGS) -D_BSD_SOURCE
+ftmod_misdn_la_CFLAGS   = $(FTDM_CFLAGS) $(AM_CFLAGS) $(MISDN_CFLAGS) -D_GNU_SOURCE
 ftmod_misdn_la_LDFLAGS  = -shared -module -avoid-version
 ftmod_misdn_la_LIBADD   = libfreetdm.la
 endif