add -znotext to kernel module link invocation

ARM kernel modules require .text relocations (DT_TEXTREL) in shared
object ouptut, which is not allowed by default by lld.  Add the -znotext
option to enable this.  For simplicity add it unconditionally: it is
already default and thus either redundant (GNU BFD ld and gold from
ports) or ignored as an unknown option (GNU BFD ld 2.17.50 in the base
system).

Reviewed by:	kib
MFC after:	3 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D11250

sys/conf/kmod.mk

@@ -210,8 +210,8 @@ ${PROG}.debug: ${FULLPROG}
 .if ${__KLD_SHARED} == yes
 ${FULLPROG}: ${KMOD}.kld
 .if ${MACHINE_CPUARCH} != "aarch64"
-	${LD} -m ${LD_EMULATION} -Bshareable ${_LDFLAGS} -o ${.TARGET} \
-	    ${KMOD}.kld
+	${LD} -m ${LD_EMULATION} -Bshareable -znotext ${_LDFLAGS} \
+	    -o ${.TARGET} ${KMOD}.kld
 .else
 #XXXKIB Relocatable linking in aarch64 ld from binutils 2.25.1 does
 #       not work.  The linker corrupts the references to the external