Move FreeBSD CFLAGS and LDFLAGS to configure

Backport of commit 09c1e370b3.

.gitlab-ci.yml

@@ -211,9 +211,6 @@ docker_ubuntu-16_04-amd64:
 
 # TODO We want to copy these BSDs to our own virtual machines, to make sure someone doesn't update them by accident.
 .freebsd-11-i386: &freebsd-11-i386_env
-  variables:
-    CPPFLAGS: "-I/usr/local/include"
-    LDFLAGS: "-L/usr/local/lib"
   tags:
   - freebsd
   - i386
@@ -223,9 +220,6 @@ docker_ubuntu-16_04-amd64:
   #- tags
 
 .freebsd-11-amd64: &freebsd-11-amd64_env
-  variables:
-    CPPFLAGS: "-I/usr/local/include"
-    LDFLAGS: "-L/usr/local/lib"
   tags:
   - freebsd
   - amd64

configure.ac

@@ -216,9 +216,13 @@ else
       ;;
     ipv6:freebsd*)
       sysdesc=bsd-v6
+      CPPFLAGS="$CPPFLAGS -I/usr/local/include"
+      LDFLAGS="$LDFLAGS -L/usr/local/lib"
       ;;
     ipv4:freebsd*)
       sysdesc=bsd
+      CPPFLAGS="$CPPFLAGS -I/usr/local/include"
+      LDFLAGS="$LDFLAGS -L/usr/local/lib"
       ;;
     ipv6:dragonfly*)
       sysdesc=bsd-v6
@@ -419,4 +423,5 @@ AC_MSG_RESULT([        Debugging:		$enable_debug])
 AC_MSG_RESULT([        POSIX threads:		$enable_pthreads])
 AC_MSG_RESULT([        Routing protocols:	$protocols])
 AC_MSG_RESULT([        Client:			$enable_client])
+
 rm -f $objdir/.*-stamp