Some more clean and stability fixes

Changes are:
- "fortification" feature (available on some implementations of glibc, on Mac for example) is suppressed in builtins/builtins.c. When not present and not suppressed it breaks __do_print() for generic targets (+5 passing generic-4 tests on Mac on my system)
- on Windows a define was added to not issue tens of warnings related to sprintf (we don't want to change the source, we just don't want to see warnings)
- MacOS has "symbol versions" feature for some library functions, which requires some special handling, it's required to make fputs() from __do_printf() work.
- cleanup in sse4.h - added some explicit conversions to avoid warnings and removed trailing spaces.
- minor fix for run_tests.py to run only single thread, when run with for single test.