fix build error on OsX 10.5

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@6251 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/mod/applications/mod_expr/Makefile

 BASE=../../../..
 LOCAL_SOURCES=expreval.c exprinit.c exprobj.c exprutil.c exprfunc.c exprmem.c exprpars.c exprval.c
 LOCAL_OBJS=expreval.o exprinit.o exprobj.o exprutil.o exprfunc.o exprmem.o exprpars.o exprval.o
-LOCAL_LIBADD=-lm
+LOCAL_LDFLAGS=-lm
 include $(BASE)/build/modmake.rules