gdc can output error messages in the system language which can break
the regex mactches the code relies on.
Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>
Change the format in which errors are printed to keep it consistent
across all the three major compilers (a style that they all support is
the gnu style) and make the matching code in generate_tests.d more
readable by using a regex.
Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>