amd64: remove caml_call_gc{1,2,3} and simplify caml_alloc{1,2,3,N}
by tail-calling caml_call_gc.
i386: simplify caml_alloc{1,2,3,N} by tail-calling caml_call_gc.
these functions do not need to preserve ebx.
arm: simplify caml_alloc{1,2,3,N} by tail-calling caml_call_gc.
partial revert of #8619.
arm64: simplify caml_alloc{1,2,3,N} by tail-calling caml_call_gc.
partial revert of #8619.
power: partial revert of #8619.
avoid restarting allocation sequence after failure.
s390: partial revert of #8619.
avoid restarting allocation seqeunce after failure.