src: link against libgnu.la for "c-ctype.h" symbols

libtasn1.la now uses functions from "c-ctype.h", which needs the
tools to be linked with libgnu.la.

Signed-off-by: Daiki Ueno <ueno@gnu.org>
diff --git a/src/Makefile.am b/src/Makefile.am
index 4459767..3dabda1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -20,7 +20,7 @@
 AM_CPPFLAGS = -I$(top_builddir)/lib/includes -I$(top_srcdir)/lib/includes \
  -I$(top_builddir)/lib/gl -I$(top_srcdir)/lib/gl $(CODE_COVERAGE_CPPFLAGS)
 
-LDADD = ../lib/libtasn1.la
+LDADD = ../lib/libtasn1.la ../lib/gl/libgnu.la
 AM_LDFLAGS = $(CODE_COVERAGE_LDFLAGS)
 
 bin_PROGRAMS = asn1Parser asn1Coding asn1Decoding