s390/vdso: drop '-fPIC' from LDFLAGS

'-fPIC' as an option to the linker does not do what it seems like it
should. With ld.bfd, it is treated as '-f PIC', which does not make
sense based on the meaning of '-f':

  -f SHLIB, --auxiliary SHLIB Auxiliary filter for shared object symbol table

When building with ld.lld (currently under review in a GitHub pull
request), it just errors out because '-f' means nothing and neither does
'-fPIC':

  ld.lld: error: unknown argument '-fPIC'

'-fPIC' was blindly copied from CFLAGS when the vDSO stopped being
linked with '$(CC)', it should not be needed. Remove it to clear up the
build failure with ld.lld.

Fixes: 2b2a258 ("s390/vdso: Use $(LD) instead of $(CC) to link vDSO")
Link: llvm/llvm-project#75643
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20240130-s390-vdso-drop-fpic-from-ldflags-v1-1-094ad104fc55@kernel.org
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: nathanchance

arch/s390/kernel/vdso32/Makefile

@@ -22,7 +22,7 @@ KBUILD_CFLAGS_32 := $(filter-out -m64,$(KBUILD_CFLAGS))
 KBUILD_CFLAGS_32 := $(filter-out -mno-pic-data-is-text-relative,$(KBUILD_CFLAGS_32))
 KBUILD_CFLAGS_32 += -m31 -fPIC -shared -fno-common -fno-builtin
 
-LDFLAGS_vdso32.so.dbg += -fPIC -shared -soname=linux-vdso32.so.1 \
+LDFLAGS_vdso32.so.dbg += -shared -soname=linux-vdso32.so.1 \
 	--hash-style=both --build-id=sha1 -melf_s390 -T
 
 $(targets:%=$(obj)/%.dbg): KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)

arch/s390/kernel/vdso64/Makefile

@@ -26,7 +26,7 @@ KBUILD_AFLAGS_64 += -m64
 KBUILD_CFLAGS_64 := $(filter-out -m64,$(KBUILD_CFLAGS))
 KBUILD_CFLAGS_64 := $(filter-out -mno-pic-data-is-text-relative,$(KBUILD_CFLAGS_64))
 KBUILD_CFLAGS_64 += -m64 -fPIC -fno-common -fno-builtin
-ldflags-y := -fPIC -shared -soname=linux-vdso64.so.1 \
+ldflags-y := -shared -soname=linux-vdso64.so.1 \
 	     --hash-style=both --build-id=sha1 -T
 
 $(targets:%=$(obj)/%.dbg): KBUILD_CFLAGS = $(KBUILD_CFLAGS_64)