amd64: do not pass -z rodynamic to ld.bfd when building vdso

Apparently newer versions of binutils complain instead of silently
ignoring the unknown -z option.

Reported by:	bz
Reviewed by:	emaste
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D47176

sys/tools/amd64_ia32_vdso.sh

@@ -34,9 +34,14 @@ ${CC} -x assembler-with-cpp -DLOCORE -fPIC -nostdinc -c -m32 \
    -o ia32_sigtramp.pico -I. -I"${S}" -include opt_global.h \
    "${S}"/amd64/ia32/ia32_sigtramp.S
 
+if ${LD} --version | ${AWK} '/^GNU ld/{exit 1}' ; then
+    RODYNAMIC="-z rodynamic"
+else
+    RODYNAMIC=""
+fi
 ${LD} --shared -Bsymbolic -soname="elf-vdso32.so.1" \
    -T "${S}"/conf/vdso_amd64_ia32.ldscript \
-   --eh-frame-hdr --no-undefined -z rodynamic -z norelro -nmagic \
+   --eh-frame-hdr --no-undefined ${RODYNAMIC} -z norelro -nmagic \
    --hash-style=sysv --fatal-warnings --strip-all \
    -o elf-vdso32.so.1 ia32_sigtramp.pico
 

sys/tools/amd64_vdso.sh

@@ -40,12 +40,17 @@ ${CC} -x assembler-with-cpp -DLOCORE -fPIC -nostdinc -c \
 #
 # -z rodynamic is undocumented lld-specific option, seemingly required
 # for lld to avoid putting dynamic into dedicated writeable segment,
-# despite ldscript placement.  It is ignored by ld.bfd but ldscript
+# despite ldscript placement.  It is omitted for ld.bfd, but ldscript
 # alone is enough there.
 #
+if ${LD} --version | ${AWK} '/^GNU ld/{exit 1}' ; then
+    RODYNAMIC="-z rodynamic"
+else
+    RODYNAMIC=""
+fi
 ${LD} --shared -Bsymbolic -soname="elf-vdso.so.1" \
    -T "${S}"/conf/vdso_amd64.ldscript \
-   --eh-frame-hdr --no-undefined -z rodynamic -z norelro -nmagic \
+   --eh-frame-hdr --no-undefined ${RODYNAMIC} -z norelro -nmagic \
    --hash-style=sysv --fatal-warnings --strip-all \
    -o elf-vdso.so.1 sigtramp.pico