* tests: Fix shellcheck warnings in playTests.sh
* tests: Do not use ../programs which is relative to tests dirs
This commit fixes error when running playTests.sh in Meson.
Mesonbuild runs out of tree, so ./datagen not in `zstd/tests` dir,
it lies in <mesonbuilddir>/tests. This leads to ../programs invalid.
* tests: Replace relative paths for zstd/tests dir
* playTests: Set shell options explicitly, not in shebang
* playTests: Replace echo -e with printf
* meson: Fix test-zstd
Use std=gnu99 to build and test just like `make test`.
* meson: Fix legacy test
* meson: Enable testing in CI
Run build under release mode for faster test time.
* meson: Increase timeout time for test-zstream
