ANDROID: syscalls/x86: use a weak function for IA32 compat syscalls

After LLVM commit rG8f8b5e5587c3 ("[MC] Error for .globl/.local which
change the symbol binding and warn for .weak"), using cond_syscall()
for IA32 compat syscalls produces the following errors with LTO:

  error: __ia32_compat_sys_sysctl changed binding to STB_GLOBAL

Avoid conflicting .weak/.globl statements by using a weak function for
the stub instead.

Bug: 180726982
Link: https://github.com/ClangBuiltLinux/linux/issues/1269


Change-Id: I52446c153155f40cefecf6230cbc0d229de02041
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>