um: vdso: Always reject undefined references in 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 <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Johannes Berg <[e-mail]>

arch/x86/um/vdso/Makefile

···
 quiet_cmd_vdso = VDSO    $@
       cmd_vdso = $(CC) -nostdlib -o $@ \
 		       $(CC_FLAGS_LTO) $(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
-		       -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^) && \
-		 sh $(src)/checkundef.sh '$(NM)' '$@'
+		       -Wl,-T,$(filter %.lds,$^) $(filter %.o,$^)
 
-VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv -z noexecstack
+VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv -z noexecstack -Wl,--no-undefined

arch/x86/um/vdso/checkundef.sh

···
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-nm="$1"
-file="$2"
-$nm "$file" | grep '^ *U' > /dev/null 2>&1
-if [ $? -eq 1 ]; then
-    exit 0
-else
-    echo "$file: undefined symbols found" >&2
-    exit 1
-fi