Reapply: move libc++ from /usr/lib to /lib

As with other runtime components like libc or libcxxrt.

If desired we can stop linking devd statically after this change (to
achive approximately no net change in required root filesystem size).

We must set SHLIBDIR with ?= before including <src.opts.mk>, otherwise
that will have set SHBLIDIR to its default value of /usr/lib.

Otherwise, "make delete-old-libs" would suggest to delete libc++.so.1
from /usr/lib, while there was not yet a copy in /lib.

Reviewed by:	imp
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D33123

ObsoleteFiles.inc

@@ -40,6 +40,9 @@
 #   xargs -n1 | sort | uniq -d;
 # done
 
+# 20211229 libc++ moved to /lib
+OLD_LIBS+=usr/lib/libc++.so.1
+
 # 20211221 efi_set_variables_supported.3 should be efi_variables_supported.3
 OLD_FILES+=usr/share/man/man3/efi_set_variables_supported.3.gz
 

lib/libc++/Makefile

@@ -1,5 +1,7 @@
 # $FreeBSD$
 
+SHLIBDIR?=	/lib
+
 .include <src.opts.mk>
 
 PACKAGE=	clibs