This patch contains two improvements over the previous version:

 * it uses configure to check whether sys/termio.h is available and uses
the result to determine whether to include it and
 * it makes malloc_closure.c use _SC_PAGESIZE instead of getpagesize if
it's available.

I believe there are two unresolved issues at this point, the wchar_t
definition and the stack size.

[n]curses.h defines wchar_t if _XOPEN_SOURCE_EXTENDED is defined and if
_WCHAR_T is not defined:

 #ifdef _XOPEN_SOURCE_EXTENDED
 #ifndef _WCHAR_T
 typedef unsigned long wchar_t;
 #endif /* _WCHAR_T */
 #ifndef _WINT_T
 typedef long int wint_t;
 #endif /* _WINT_T */

stdlib.h defines wchar_t if __WCHAR_T is defined:

 #if defined(__WCHAR_T)
 typedef __WCHAR_T       wchar_t;
 #undef __WCHAR_T
 #endif

I'm afraid I don't quite understand what configure should test for in
this case either.  Please help!

Regarding the stack size, how can I test whether 2MiB is sufficient for
the default recursion limit?