powerpc/boot/wrapper: Add "-z rodynamic" when using LLD

Normally all read-only sections precede SHF_WRITE sections. .dynamic
and .got have the SHF_WRITE flag; .dynamic probably because of
DT_DEBUG. LLD emits an error when this happens, so use "-z rodynamic"
to mark .dynamic as read-only.
Signed-off-by: Bill Wendling <morbo@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201118223910.2711337-1-morbo@google.com

arch/powerpc/boot/wrapper

@@ -46,6 +46,7 @@ compression=.gz
 uboot_comp=gzip
 pie=
 format=
+rodynamic=
 
 # cross-compilation prefix
 CROSS=
@@ -353,6 +354,7 @@ epapr)
     platformo="$object/pseries-head.o $object/epapr.o $object/epapr-wrapper.o"
     link_address='0x20000000'
     pie=-pie
+    rodynamic=$(if ${CROSS}ld -V 2>&1 | grep -q LLD ; then echo "-z rodynamic"; fi)
     ;;
 mvme5100)
     platformo="$object/fixed-head.o $object/mvme5100.o"
@@ -493,7 +495,7 @@ if [ "$platform" != "miboot" ]; then
         text_start="-Ttext $link_address"
     fi
 #link everything
-    ${CROSS}ld -m $format -T $lds $text_start $pie $nodl -o "$ofile" $map \
+    ${CROSS}ld -m $format -T $lds $text_start $pie $nodl $rodynamic -o "$ofile" $map \
 	$platformo $tmp $object/wrapper.a
     rm $tmp
 fi