[armv7 fix] security/botan2

Fixed building on armv7 by disabling neon support in configure. This has
no effect on amd64. I tested a build there and all tests passed. 16 tests
failed on armv7, all unable to allocate lzma memory if I remember
correctly.

Index: Makefile
===================================================================
RCS file: /cvs/ports/security/botan2/Makefile,v
retrieving revision 1.16
diff -u -p -r1.16 Makefile
--- Makefile 12 Apr 2018 09:53:54 -0000 1.16
+++ Makefile 30 Apr 2018 07:28:24 -0000
@@ -39,6 +39,7 @@ CONFIGURE_ARGS = --with-build-dir=${WRKB
--prefix=${PREFIX} \
--distribution-info="`uname -sr`" \
--mandir=${PREFIX}/man \
+ --disable-neon \
--with-bzip2 \
--with-lzma \
--with-openssl \