Fix linker error: link all examples against gnutls when available

The library now uses GnuTLS functions (gnutls_malloc, gnutls_free,
gnutls_hex2bin) for PSK support, so all examples need to link against
gnutls when HAVE_GNUTLS is defined, not just the PSK example.

Author: etr

examples/Makefile.am

@@ -44,7 +44,7 @@ benchmark_nodelay_SOURCES = benchmark_nodelay.cpp
 file_upload_SOURCES = file_upload.cpp
 
 if HAVE_GNUTLS
+LDADD += -lgnutls
 noinst_PROGRAMS += minimal_https_psk
 minimal_https_psk_SOURCES = minimal_https_psk.cpp
-minimal_https_psk_LDADD = $(LDADD) -lgnutls
 endif