GoogleTest, starting with vesion 1.13.0, requires C++14 to build. This
patch enables C++14 if GoogleTest 1.13.0 or newer is detected when
compiling the tests with Meson, making it possible to use new GTest
versions.
You can find GoogleTest's release notes at
<https://github.com/google/googletest/releases/tag/v1.13.0>.
Meson only runs required targets. The key_encrypted_pem and
cert_encrypted_pem targets added in 020b0db090
and 8191fd8e6c weren't added to the list
of targets required by the test target, so the generation of the
encrypted certs was skipped, resulting in the failure of
BindServerTest.BindAndListenSeparatelySSLEncryptedKey.
This integrates the "main" test suite (test/test.cc) in Meson.
This allows to run the tests in the CI with the Meson-built version of
the library to ensure that nothing breaks unexpectedly.
It also simplifies life of downstream packagers, that do not have to
write a custom build script to split the library and run tests but can
instead just let Meson do that for them.
