USES=localbase:ldflags can be used to set LDFLAGS. Normally LDFLAGS
appears too early on the command line causing some ports to link with
their own libraries in LOCALBASE (if installed) instead of WRKSRC.
Also make use of _USES_POST so -L${LOCALBASE}/lib is added as late as
possible after anything a port Makefile might set. Use _USES_POST
instead of .include in libedit.mk and libarchive.mk so things like
'USES=libedit localbase:ldflags' work correctly.
Fix some issues with LIBS in some ports.
Switch ports that don't support LIBS to localbase:ldflags.
PR: 212987
Exp-run by: antoine
Approved by: portmgr (antoine)
