elf: Ignore LD_PROFILE for setuid binaries

elf: Ignore LD_PROFILE for setuid binaries

Loader does not ignore LD_PROFILE in secure-execution mode (different
than man-page states [1]), rather it uses a different path
(/var/profile) and ignore LD_PROFILE_OUTPUT.

Allowing secure-execution profiling is already a non good security
boundary, since it enables different code paths and extra OS access by
the process.  But by ignoring LD_PROFILE_OUTPUT, the resulting profile
file might also be acceded in a racy manner since the file name does not
use any process-specific information (such as pid, timing, etc.).

Another side-effect is it forces lazy binding even on libraries that
might be with DF_BIND_NOW.

[1] https://man7.org/linux/man-pages/man8/ld.so.8.html
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>