Merge from matt-nb5-mips64.

branches: 1.5.46;
Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22280, verified by myself.

ABICALLS -> __ABICALLS__

branches: 1.3.2;
Remove all the .abicalls assembler directives - "SYS.h" already has that.

* On architectures using ELF, and conditionally on those in transition, rename
_ASM_LABEL(cerror) and _ASM_LABEL(curbrk) to _C_LABEL(__cerror) and
_C_LABEL(__curbrk) (or their respective architecture-specific equivalents) to
avoid possible name clashes with identifiers used in user applications.
* Do the same for minbrk on all architectures to avoid a GCC-specific (and
on ELF architectures effectively useless) symbol reference renaming in MI code.

Add syscall stubs for __vfork14(). These are basically copies of Ovfork.S
with the syscall numbers changed.

Since 4.4BSD vfork(2) did not share address space, Ovfork.S could be changed
to be identical to fork.S (modulo syscall numbers). __vfork14.S, however,
needs to remain separate since with a shared address space, the stub needs to
pre-decrement the stack and do an indirect jump to the return address, so that
the shared stackframe is still there when the parent returns. (Obviously,
this does not apply to systems which to not build stackframes on leaf calls.)