Compile with language C by default

Compile with language C by default.

This should enable easier use with macOS.

• Added command line options, seen with compile-gvec-tp -h
• The "--compiler" option can now take the four compilers available in pyccel ("GNU" is the default, "intel", "PGI", "nvidia"). Moreover, a JSON file can be specified to define a custom compiler (see pyccel doc).

assigned to @spossann

enabled an automatic merge when the pipeline for 1b1317c7 succeeds

canceled the automatic merge

mentioned in commit d2c87885

merged