x86/vdso: Always reject undefined references during linking

Instead of using a custom script to detect and fail on undefined
references, use --no-undefined for all VDSO linker invocations.

Drop the now unused checkundef.sh script.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250306-vdso-checkundef-v2-1-a26cc315fd73@linutronix.de

arch/x86/entry/vdso/Makefile

@@ -32,7 +32,7 @@ targets += $(foreach x, 64 x32 32, vdso-image-$(x).c vdso$(x).so vdso$(x).so.dbg
 
 CPPFLAGS_vdso.lds += -P -C
 
-VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-undefined \
+VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 \
 			-z max-page-size=4096
 
 $(obj)/vdso64.so.dbg: $(obj)/vdso.lds $(vobjs) FORCE
@@ -151,10 +151,9 @@ $(obj)/vdso32.so.dbg: $(obj)/vdso32/vdso32.lds $(vobjs32) FORCE
 quiet_cmd_vdso = VDSO    $@
       cmd_vdso = $(LD) -o $@ \
 		       $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
-		       -T $(filter %.lds,$^) $(filter %.o,$^) && \
-		 sh $(src)/checkundef.sh '$(NM)' '$@'
+		       -T $(filter %.lds,$^) $(filter %.o,$^)
 
-VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
+VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 --no-undefined \
 	$(call ld-option, --eh-frame-hdr) -Bsymbolic -z noexecstack
 
 quiet_cmd_vdso_and_check = VDSO    $@