RISC-V: build vdso-dummy.o with -no-pie

Debian toolcahin defaults to PIE, and I guess that will also be the case
of most distributions. This causes the following build failure:

  AS      arch/riscv/kernel/vdso/getcpu.o
  AS      arch/riscv/kernel/vdso/flush_icache.o
  VDSOLD  arch/riscv/kernel/vdso/vdso.so.dbg
  OBJCOPY arch/riscv/kernel/vdso/vdso.so
  AS      arch/riscv/kernel/vdso/vdso.o
  VDSOLD  arch/riscv/kernel/vdso/vdso-dummy.o
  LD      arch/riscv/kernel/vdso/vdso-syms.o
riscv64-linux-gnu-ld: attempted static link of dynamic object `arch/riscv/kernel/vdso/vdso-dummy.o'
make[2]: *** [arch/riscv/kernel/vdso/Makefile:43: arch/riscv/kernel/vdso/vdso-syms.o] Error 1
make[1]: *** [scripts/Makefile.build:575: arch/riscv/kernel/vdso] Error 2
make: *** [Makefile:1018: arch/riscv/kernel] Error 2

While the root Makefile correctly passes "-fno-PIE" to build individual
object files, the RISC-V kernel also builds vdso-dummy.o as an
executable, which is therefore linked as PIE. Fix that by updating this
specific link rule to also include "-no-pie".
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/vdso/Makefile

@@ -52,7 +52,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
 # Add -lgcc so rv32 gets static muldi3 and lshrdi3 definitions.
 # Make sure only to export the intended __vdso_xxx symbol offsets.
 quiet_cmd_vdsold = VDSOLD  $@
-      cmd_vdsold = $(CC) $(KCFLAGS) -nostdlib $(SYSCFLAGS_$(@F)) \
+      cmd_vdsold = $(CC) $(KCFLAGS) $(call cc-option, -no-pie) -nostdlib $(SYSCFLAGS_$(@F)) \
                            -Wl,-T,$(filter-out FORCE,$^) -o $@.tmp -lgcc && \
                    $(CROSS_COMPILE)objcopy \
                            $(patsubst %, -G __vdso_%, $(vdso-syms)) $@.tmp $@