add .gnu.warning.SYMBOL support to ld.lld(1) to display the warnings in

add .gnu.warning.SYMBOL support to ld.lld(1) to display the warnings in
these sections like ld.bfd(1)

e.g:
add.c(add.o:(add)): warning: sprintf() is often misused, please use snprintf()
add.c(add.o:(add)): warning: strcpy() is almost always misused, please use strlcpy()
add.c(add.o:(add)): warning: strcat() is almost always misused, please use strlcat()

ok deraadt@