GNUmakefile: Avoid building shared poser lib

When bundling poser, avoid building the shared lib by also setting
posercore_STRIPWITH empty. This issue was hidden by broken library
stripping in the earlier zimk version.

GNUmakefile

@@ -56,6 +56,7 @@ include zimk/zimk.mk
 ifeq ($(BUNDLED_POSER),1)
 WITH_TLS:=		0
 posercore_BUILDWITH:=	#
+posercore_STRIPWITH:=	#
 posercore_INSTALLWITH:=	#
 posercore_PRECFLAGS:=	-I./poser/include
 $(call zinc,poser/src/lib/core/core.mk)