Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC: r236338, r236339, r236346, r236347, r236365, & r236977
* Deprecate the FreeBSD make's ":U" (to-upper case) and ":L" (to-lower case)
modifiers for ":tu" and ":tl".
* make it easier to test newly-built make.
* Add "-V '${VAR}'" variable expansion from Portable Berkeley Make.
* regression test for '-V' command line option and the :t[lu] modifiers.

Add a test for the :tl & :tu modifiers.