meson: Run build-time tests with --tap where supported

This makes it easier to debug test failures, by ensuring that g_debug()
and g_test_message() are printed as TAP diagnostics.

Fixes: GNOME/glib#1528
Signed-off-by: Simon McVittie <smcv@collabora.com>
10 jobs for <span class="ref-name">1528-build-time-tap</span> in 25 minutes and 31 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #111344
cross-android_api21_arm64

00:01:36

passed #111345
cross-android_api28_arm64

00:01:36

passed #111346
cross-mingw64

00:02:14

passed #111343
fedora-autotools-x86_64

00:05:44

passed #111522
fedora-x86_64

00:04:35

manual #111349
freebsd-11 allowed to fail manual
freebsd-11-x86_64
passed #111347
win32
msys2-mingw32

00:07:38

passed #111348
win32
vs2017-x64

00:07:10

failed #111342
fedora-x86_64

00:04:11

 
  Coverage
passed #111350
coverage

00:02:06

74.6%