MFC r287436:

Avoid sub-shell for realpath(1) for bmake by using its built-in :tA.

MFC r272282,r272363,r272383:

r272282:
Search for the nearest PORTSDIR where Mk/bsd.ports.mk exists, from .CURDIR.
This will only take effect if PORTSDIR is not set, as previously supported.

r272363:
Always resolve PORTSDIR to absolute paths using realpath(1).

r272383:
Revise r272363 by collapsing the tests into a for loop.

Relnotes: yes

MFC r287436:

Avoid sub-shell for realpath(1) for bmake by using its built-in :tA.

MFC r272282,r272363,r272383:

r272282:
Search for the nearest PORTSDIR where Mk/bsd.ports.mk exists, from .CURDIR.
This will only take effect if PORTSDIR is not set, as previously supported.

r272363:
Always resolve PORTSDIR to absolute paths using realpath(1).

r272383:
Revise r272363 by collapsing the tests into a for loop.

Relnotes: yes