ANDROID: x86/vdso: disable LTO only for VDSO

Instead of disabling LTO for all the code in the directory, only
disable it for the VDSO itself.

Bug: 145297900
Change-Id: I95a9c68ee76fdc8f4cee5c5bd1356fc90de1680c
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
(cherry picked from commit 74d07ccc220bb807a590c7a260fa8f388ccd2af7)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 154668398