FROMLIST: x86/boot/compressed: Force hidden visibility for all symbol references

Eliminate all GOT entries in the decompressor binary, by forcing hidden
visibility for all symbol references, which informs the compiler that
such references will be resolved at link time without the need for
allocating GOT entries.

To ensure that no GOT entries will creep back in, add an assertion to
the decompressor linker script that will fire if the .got section has
a non-zero size.

[Arvind: fixup -include hidden.h to -include $(srctree)/$(src)/hidden.h]

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
From: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20200523120021.34996-3-ardb@kernel.org


Bug: 167402429
Signed-off-by: Alistair Delva <adelva@google.com>
Change-Id: I1e59843c301f3a8fe3f7e4cd7fb6906aa59383b1