s390/vdso: Generate unwind information for C modules

GDB fails to unwind vDSO functions with error message "PC not saved",
for instance when stepping through gettimeofday().

Add -fasynchronous-unwind-tables to CFLAGS to generate .eh_frame
DWARF unwind information for the vDSO C modules.

Fixes: 4bff8cb5 ("s390: convert to GENERIC_VDSO")
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/kernel/vdso32/Makefile

@@ -20,7 +20,8 @@ KBUILD_AFLAGS_32 += -m31 -s
 
 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
+KBUILD_CFLAGS_32 := $(filter-out -fno-asynchronous-unwind-tables,$(KBUILD_CFLAGS_32))
+KBUILD_CFLAGS_32 += -m31 -fPIC -shared -fno-common -fno-builtin -fasynchronous-unwind-tables
 
 LDFLAGS_vdso32.so.dbg += -shared -soname=linux-vdso32.so.1 \
 	--hash-style=both --build-id=sha1 -melf_s390 -T

arch/s390/kernel/vdso64/Makefile

@@ -26,7 +26,8 @@ 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 := $(filter-out -munaligned-symbols,$(KBUILD_CFLAGS_64))
-KBUILD_CFLAGS_64 += -m64 -fPIC -fno-common -fno-builtin
+KBUILD_CFLAGS_64 := $(filter-out -fno-asynchronous-unwind-tables,$(KBUILD_CFLAGS_64))
+KBUILD_CFLAGS_64 += -m64 -fPIC -fno-common -fno-builtin -fasynchronous-unwind-tables
 ldflags-y := -shared -soname=linux-vdso64.so.1 \
 	     --hash-style=both --build-id=sha1 -T