arm64: vdso: Add --eh-frame-hdr to ldflags

LLVM's unwinder depends on the .eh_frame_hdr being present for
unwinding. However, when compiling Linux with GCC, the section
is not present in the vdso library object and when compiling
with Clang, it is present, but it has zero length.

With GCC the problem was not spotted because libgcc unwinder does
not require the .eh_frame_hdr section to be present.

Add --eh-frame-hdr to ldflags to correctly generate and populate
the section for both GCC and LLVM.

Fixes: 28b1a82 ("arm64: vdso: Substitute gettimeofday() with C implementation")
Reported-by: Tamas Zsoldos <[email protected]>
Signed-off-by: Vincenzo Frascino <[email protected]>
Tested-by: Tamas Zsoldos <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

arch/arm64/kernel/vdso/Makefile

@@ -22,7 +22,7 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
 # routines, as x86 does (see 6f121e548f83 ("x86, vdso: Reimplement vdso.so
 # preparation in build-time C")).
 ldflags-y := -shared -nostdlib -soname=linux-vdso.so.1 --hash-style=sysv \
-		-Bsymbolic --build-id -n -T
+		-Bsymbolic --eh-frame-hdr --build-id -n -T
 
 ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18
 ccflags-y += -DDISABLE_BRANCH_PROFILING