override _PATH_SSL_CA_FILE with OPENSSLDIR at build time

fix #160

patches/tls_internal.h.patch

@@ -0,0 +1,12 @@
+--- ./openbsd/src/lib/libtls/tls_internal.h	Thu Oct 15 16:12:24 2015
++++ ./tls/tls_internal.h	Sun Dec  6 20:18:17 2015
+@@ -24,7 +24,9 @@
+ 
+ #include <openssl/ssl.h>
+ 
++#ifndef _PATH_SSL_CA_FILE
+ #define _PATH_SSL_CA_FILE "/etc/ssl/cert.pem"
++#endif
+ 
+ #define TLS_CIPHERS_COMPAT	"ALL:!aNULL:!eNULL"
+ #define TLS_CIPHERS_DEFAULT	"TLSv1.2+AEAD+ECDHE:TLSv1.2+AEAD+DHE"

tls/Makefile.am

@@ -8,6 +8,13 @@ EXTRA_DIST += CMakeLists.txt
 libtls_la_LDFLAGS = -version-info @LIBTLS_VERSION@ -no-undefined
 libtls_la_LIBADD = ../crypto/libcrypto.la ../ssl/libssl.la $(PLATFORM_LDADD)
 
+libtls_la_CPPFLAGS = $(AM_CPPFLAGS)
+if OPENSSLDIR_DEFINED
+libtls_la_CPPFLAGS += -D_PATH_SSL_CA_FILE=\"@OPENSSLDIR@\"
+else
+libtls_la_CPPFLAGS += -D_PATH_SSL_CA_FILE=\"$(sysconfdir)/ssl\"
+endif
+
 libtls_la_SOURCES = tls.c
 libtls_la_SOURCES += tls_client.c
 libtls_la_SOURCES += tls_config.c