Update the configuration for Travis CI and AppVeyor CI

Update the Travis CI matrix:
 * Run ASan and UBSan unconditionally on FreeBSD and Linux, and
   not at all on Mac.
 * Remove the `CI_NO_TEST=1` runs from the environment column.

Update the AppVeyor CI matrix:
 * Replace `CI_NO_TEST=1` with `CI_CMAKE_VARS=-DPNG_TESTS=0` when
   testing Visual Studio on ARM64.

Also apply minor stylistic changes.
2 files changed