x86/vdso: Pass --eh-frame-hdr to the linker

Commit

  379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")

accidentally broke unwinding from userspace, because ld would strip the
.eh_frame sections when linking.

Originally, the compiler would implicitly add --eh-frame-hdr when
invoking the linker, but when this Makefile was converted from invoking
ld via the compiler, to invoking it directly (like vmlinux does),
the flag was missed. (The EH_FRAME section is important for the VDSO
shared libraries, but not for vmlinux.)

Fix the problem by explicitly specifying --eh-frame-hdr, which restores
parity with the old method.

See relevant bug reports for additional info:

  https://bugzilla.kernel.org/show_bug.cgi?id=201741
  https://bugzilla.redhat.com/show_bug.cgi?id=1659295

Fixes: 379d98ddf413 ("x86: vdso: Use $LD instead of $CC to link")
Reported-by: Florian Weimer <[email protected]>
Reported-by: Carlos O'Donell <[email protected]>
Reported-by: "H. J. Lu" <[email protected]>
Signed-off-by: Alistair Strachan <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Tested-by: Laura Abbott <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Carlos O'Donell <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: [email protected]
Cc: Laura Abbott <[email protected]>
Cc: stable <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: X86 ML <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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