MFC r285119,r292502,r295380:

r285119 (by jmmv):

Add support for TEST_METADATA

Allow Makefiles to define generic metadata settings that apply to all test
programs defined by a Makefile. The generic TEST_METADATA variable extends
the per-test program settings already supported via TEST_METADATA.<program>.

This feature will be useful to easily apply some settings to all programs
in a directory. In particular, Kyua 0.12 will support parallel execution
of test programs and a bunch of them will need to be tagged as is_exclusive
to indicate that they cannot be run in parallel with anything else due to
their side-effects. It will be reasonable to set this setting on whole
directories.

r292502:

Always expose LOCALBASE, not just when CROSS_TOOLCHAIN is defined

Instead of using which(1) to look for doxygen, look for it in <LOCALBASE>/bin .
$PATH gets mangled by make buildenv, etc so it's better to just be explicit
about the path if someone uses that for instance.

r295380:

Simplify running the FreeBSD test suite

Replace make regress (legacy test make target) and make test (incomplete
test make target added with the FreeBSD test suite) with make check as it's
consistent with other open source projects.

make check defaults to running tests from .OBJDIR, but can be overridden
with the CHECKDIR variable.

Add make checkworld target to simplify running the FreeBSD test suite from
TESTSBASE (i.e. the top-level tests directory), similar to buildworld.

Document make check and make checkworld in build(7).

Other minor changes:

• Rename intermediate file (Kyuafile.auto) to Kyuafile to simplify make check.
• Remove terse warnings attached to beforetest/aftertest.
• Add kyua binary check to check target in suite.test.mk; error out if it's not found

The MFC is [partly] contingent on other build related changes being MFCed.

X-MFC to: stable/10
Relnotes: yes