Don't override LDFLAGS set in bsd.cpu.mk.

This is a direct commit to a generated file.  Simon plans to fix this
upstream before the next import.

PR:		231557
Approved by:	re (gjb)
Obtained from:	CheriBSD
Sponsored by:	DARPA, AFRL

usr.bin/bmake/Makefile.config

@@ -16,7 +16,7 @@ DEFAULT_SYS_PATH?= .../share/mk:/usr/share/mk
 
 CPPFLAGS+= 
 CFLAGS+= ${CPPFLAGS} -DHAVE_CONFIG_H
-LDFLAGS= 
+LDFLAGS+= 
 LIBOBJS=  ${LIBOBJDIR}stresep$U.o
 LDADD= 
 USE_META= yes