ANDROID: arm64: fix function types in COND_SYSCALL

Define a weak function for COND_SYSCALL instead of creating a weak
alias to a function with an incompatible type. This fixes indirect
call mismatches with Control-Flow Integrity.

Bug: 138254717
Change-Id: I3a9a8162f30ff63cea2002304f70152b7cc8f746
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>