Rewrite detection of VA_LIST_IS_ARRAY.

I'm not sure exactly why Python needs this (is it only a memcpy()
optimization?)

But osh now works on the 'ubuntu32' VM!

Python-2.7.13/pyconfig.h

@@ -1013,9 +1013,6 @@
/* Define if you want to use MacPython modules on MacOSX in unix-Python. */
/* #undef USE_TOOLBOX_OBJECT_GLUE */

/* Define if a va_list is an array of some kind */
#define VA_LIST_IS_ARRAY 1

/* Define if you want SIGFPE handled (see Include/pyfpe.h). */
/* #undef WANT_SIGFPE_HANDLER */

configure

@@ -229,6 +229,19 @@ detect_c_language() {
  # TODO: Detect header and size.
  echo '#define HAVE_WCHAR_H 1'
  echo '#define SIZEOF_WCHAR_T 4'

  cat >$TMP/detect_va_list.c <<EOF
#include <stdarg.h>  /* C89 */
int main() {
  va_list list1, list2;
  list1 = list2;
}
EOF
  if cc_quiet $TMP/detect_va_list.c; then
    echo ''  # not an array
  else
    echo '#define VA_LIST_IS_ARRAY 1'
  fi
}

# Another way of working: set detected-config.mk ?