HBSD: Add RELRO Support

github-issue: #40

This adds support for RELRO and BINDNOW in the build system. This
patch was obtained from Baptiste Darroussin from his patch submitted
to FreeBSD Phabricator. Further work will need to happen in the ports
tree.

Obtained-from: Baptiste Daroussin (bapt@freebsd.org)
Obtained-from: FreeBSD Phabricator - https://reviews.freebsd.org/D3001

Signed-off-by: Shawn Webb <shawn.webb@hardenedbsd.org>

share/mk/bsd.lib.mk

@@ -58,6 +58,8 @@ SHARED_CXXFLAGS+= -g
 CTFFLAGS+= -g
 .endif
 
+LDFLAGS+=	-Wl,-z,relro  -Wl,-z,now
+
 .include <bsd.libnames.mk>
 
 # prefer .s to a .c, add .po, remove stuff not used in the BSD libraries

share/mk/bsd.prog.mk

@@ -19,6 +19,8 @@ LDFLAGS+= -pie
 .endif
 .endif
 
+LDFLAGS+=	-Wl,-z,relro  -Wl,-z,now
+
 .if ${MK_ASSERT_DEBUG} == "no"
 CFLAGS+= -DNDEBUG
 NO_WERROR=