chore: add filc compile target

[steve-chavez]

Uses https://github.com/mbrock/filnix to do this.

[steve-chavez]

fil-c fails with an interesting error:

=== TEST: basic parsers

filc safety error: cannot read pointer with null object.
    pointer: 0x10,<null>
    expected 8 bytes.
semantic origin:
    (basic) <somewhere>: cpc_basic_test_run
check scheduled at:
    (basic) <somewhere>: cpc_basic_test_run
    (basic) <somewhere>: main
    (libc.so.6666) ../sysdeps/nptl/libc_start_call_main.h:58:16: __libc_start_call_main
    (libc.so.6666) ../csu/libc-start.c:161:3: __libc_start_main
    (libpizlo.so) <runtime>: start_program
[3397] filc panic: thwarted a futile attempt to violate memory safety.
./test/test.sh: line 13:  3397 Trace/breakpoint trap   (core dumped) ./build/basic

[steve-chavez]

So the underlying bug (676d272) was not surfaced with gcc because of the optimizer dead code elimination, we compiled with -O3. Now with -O0 (043832f) a segfault appears with gcc and clang too.

---

The freestanding test fails on clang, see #12, for now we skip this test ( 248bdb5)