tests: add `exec.skip` to compile but not execute tests

Signed-off-by: Jean Privat <jean@pryen.org>
tests: niti fully skips tests in exec.skip

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add `cc.skip` to skip the C compilation of some programs

Exemple: unavailable C libraries.

Signed-off-by: Jean Privat <jean@pryen.org>
model: fatal error, instead of abort if more that one primitive class

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add missing sav

Signed-off-by: Jean Privat <jean@pryen.org>
tests: a res without sav is OK if empty else is failed

This will simplify the addition of sav, that are required only if not
empty.
Moreover, a missing non-empty sav will triggers a FAIL instead of a
skip.

Signed-off-by: Jean Privat <jean@pryen.org>
tests: remove empty sav files

since now, empty res and no sav is an OK test

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add more stuff from examples and contrib

Thanks to the cc.skip and exec.skip files, suitable tests are available

Signed-off-by: Jean Privat <jean@pryen.org>
Merge: tests: better handling of tests without a sav file

In tests, do not tag tests without sav files with *skipped*.
Instead: an empty `.res` file is a *success*, otherwise a non-empty `.res` is a *failure*.

In order to enable the correct behavior for all tests, two special `.skip` files are added to catch regressions in the Nit code.

`cc.skip` skips the C compilation and is used for programs that require a specific but unavailable C library.
Tests in this file are compiled with the `--no-cc` option.

`exec.skip` skips the execution and is used for program whose execution is unsuitable or unreproducible.
Programs that rely on the environ var `NIT_TESTING` in their code may want to drop it and just add themselves to the `exec.skip`

Pull-Request: #423
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>