BACKPORT: arm64: vdso: Add '-Bsymbolic' to ldflags

Commit 28b1a824a4f44 ("arm64: vdso: Substitute gettimeofday() with C
implementation") introduced an unused 'VDSO_LDFLAGS' variable to the
vdso Makefile, suggesting that we should be passing '-Bsymbolic' to the
linker, as we do when linking the compat vDSO.

Although it's not strictly necessary to pass this flag, it would be
required if we were to add any internal references to the exported
symbols. It's also consistent with how we link the compat vdso so, since
there's no real downside from passing it, add '-Bsymbolic' to the ldflags
for the native vDSO.

Bug: 254441685
Fixes: 28b1a824a4f44 ("arm64: vdso: Substitute gettimeofday() with C implementation")
Reported-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20200428150854.33130-1-vincenzo.frascino@arm.com


Signed-off-by: Will Deacon <will@kernel.org>
(cherry picked from commit 86b8783701246a22a734824674cc3f87a5ed9f13)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I99010ff671c8b33bfbaa1c9da52a12a3dbc7bdf0