On powerpc, pull in devel/libatomic, so that this package builds.

Build fix only for this platform; detection for -latomic is already there.
OK'ed by gdt@

databases/mysql57-client/hacks.mk

@@ -0,0 +1,12 @@
+# $NetBSD: hacks.mk,v 1.1 2020/09/22 19:39:26 he Exp $
+
+.if !defined(MYSQL_HACKS_MK)
+MYSQL_HACKS_MK=	defined
+
+# [Tue Sep 22 21:38:02 CEST 2020 : he]
+# On NetBSD/powerpc, use devel/libatomic to get 8-byte atomics.
+.if ${MACHINE_ARCH} == "powerpc"
+.include "../../devel/libatomic/buildlink3.mk"
+.endif
+
+.endif	# MYSQL_HACKS_MK