Disable NEON and ARMv8 optimizations.

Should address PR pkg/52444 reported by Marek Benc.

Index: Makefile
===================================================================
RCS file: /cvsroot/pkgsrc/security/libgcrypt/Makefile,v
retrieving revision 1.91
diff -u -p -r1.91 Makefile
--- Makefile	23 Jul 2017 17:27:52 -0000	1.91
+++ Makefile	31 Jul 2017 09:02:53 -0000
@@ -54,6 +54,11 @@ CONFIGURE_ENV+=		gcry_cv_gcc_inline_asm_
 .  endif
 .endif
 
+.if ${MACHINE_ARCH} == "arm"
+CONFIGURE_ARGS+=	--disable-neon-support
+CONFIGURE_ARGS+=	--disable-arm-crypto-support
+.endif
+
 SUBST_CLASSES+=		rpath
 SUBST_FILES.rpath=	src/libgcrypt-config.in
 SUBST_STAGE.rpath=	pre-configure