Use -znorelro for kernel modules, when they are linked as shared

binaries (e.g. on any arch except amd64 and mips).

Otherwise, with lld 9, after https://reviews.llvm.org/rLLD356117, the
modules will get an additional PT_LOAD segment, which blows up kldxref,
since that has a hardcoded limit of 3 segments.

I could have alternatively bumped up that limit, but since kernel
modules do not use relro, the simplest workaround is to explicitly
disable it.

sys/conf/kmod.mk

@@ -230,7 +230,7 @@ ${PROG}.debug: ${FULLPROG}
 
 .if ${__KLD_SHARED} == yes
 ${FULLPROG}: ${KMOD}.kld
-	${LD} -m ${LD_EMULATION} -Bshareable -znotext ${_LDFLAGS} \
+	${LD} -m ${LD_EMULATION} -Bshareable -znotext -znorelro ${_LDFLAGS} \
 	    -o ${.TARGET} ${KMOD}.kld
 .if !defined(DEBUG_FLAGS)
 	${OBJCOPY} --strip-debug ${.TARGET}