rc.d/ldconfig: Prepend rtld stdlib paths to ldconfig(32)_paths

Ensure that ldconfig-managed elf and elf32 hints always include
the standard library paths that are known independently to rtld.

PR:			275031
Reviewed by:		kib
MFC after:		2 weeks
Sponsored by:		Saltant Solutions LLC
Differential Revision:	https://reviews.freebsd.org/D42557

libexec/rc/rc.d/ldconfig

@@ -22,7 +22,7 @@ ldconfig_start()
 	ldconfig=${ldconfig_command}
 	checkyesno ldconfig_insecure && _ins="-i"
 	if [ -x "${ldconfig_command}" ]; then
-		_LDC="/lib /usr/lib"
+		_LDC=$(/libexec/ld-elf.so.1 -v | sed -n -e '/^Default lib path /s///p' | tr : ' ')
 		for i in ${ldconfig_local_dirs}; do
 			if [ -d "${i}" ]; then
 				_files=`find ${i} -type f`
@@ -52,6 +52,9 @@ ldconfig_start()
 				fi
 			done
 			_LDC=""
+			if [ -x /libexec/ld-elf32.so.1 ]; then
+				_LDC=$(/libexec/ld-elf32.so.1 -v | sed -n -e '/^Default lib path /s///p' | tr : ' ')
+			fi
 			for i in ${ldconfig32_paths}; do
 				if [ -r "${i}" ]; then
 					_LDC="${_LDC} ${i}"