linux: Inline __syscall_internal_cancel and __syscall_cancel

linux: Inline __syscall_internal_cancel and __syscall_cancel

It improves some interception tools such as valgrind, however on
multithread the __syscall_cancel_arch is called.

The result libc.so has a slight larger code size:

ABI             master        patched         diff        increase
aarch64        1658673        1669121        10448           0.63%
x86_64         1976656        1985744         9088           0.46%
i686           2233622        2251130        17508           0.78%
powerpc64le    2382448        2396768        14320           0.60%

It mimics internally how cancellable entrypoints were implemented
before 89b53077d2a58f00e7debdfe58afabe953dac60d, where cancellation
handlign were done inline in the syscall wraper.