Sure, Look in the function.....
check_force_ascii()
You'll see a hunk of code that is ifdef'd for ...
#if defined(HAVE_LANGINFO_H) && defined(CODESET)
Then you'll see
setlocale()
is called outside of that check, just before another hunk of code is
ifdef'd with the same....
#if defined(HAVE_LANGINFO_H) && defined(CODESET)
Basically making setlocale() outside of the check, and therefore requiring the #include <locale.h> outside of the above check as well.
In pythonrun.c the setlocale() call is already wrapped inside the #ifdef so the problem is bumped into there.