libcrypto: Copy the arm64 header when building asm

It may be needed when it's updated so is best to keep in sync with the
assembly files.

Reviewed by:	emaste
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D41938

secure/lib/libcrypto/Makefile.asm

@@ -46,6 +46,7 @@ ASM=	${SRCS:R:S/$/.S/} sha256-armv8.S
 
 all:	${ASM}
 	rm -f ${ASM:R:S/$/.s/}
+	${CP} ${LCRYPTO_SRC}/crypto/arm_arch.h arm_arch.h
 
 CLEANFILES=	${ASM}
 .SUFFIXES:	.pl