libc: don't directly link libsys

It is sufficent to add it as a filter.

Reported by:	kib
Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D43781

lib/libc/Makefile

@@ -62,7 +62,6 @@ CFLAGS+= -ftls-model=initial-exec
 #
 LDFLAGS+= -nodefaultlibs
 LIBADD+=	compiler_rt
-LIBADD+=	sys
 
 LDFLAGS+=-Wl,--auxiliary,libsys.so.7
 

share/mk/src.libnames.mk

@@ -393,7 +393,7 @@ _DP_xo=		util
 _DP_ztest=	geom m nvpair umem zpool pthread avl zfs_core spl zutil zfs uutil icp
 # The libc dependencies are not strictly needed but are defined to make the
 # assert happy.
-_DP_c=		sys compiler_rt
+_DP_c=		compiler_rt
 # Use libssp_nonshared only on i386 and power*.  Other archs emit direct calls
 # to __stack_chk_fail, not __stack_chk_fail_local provided by libssp_nonshared.
 .if ${MK_SSP} != "no" && \