Problem with AC_CHECK_TYPE on MacOS X

[Reuben Thomas]

In some autoconf code generated by gnulib, a conftest.h is created that 
contains the following line:

#define size_t unsigned int

Unfortunately, this causes a compilation failure, as the system stdio.h, 
which is included in ac_includes_default and hence the relevant test, 
contains the code:

#ifndef _SIZE_T
#define _SIZE_T
typedef __darwin_size_t         size_t;
#endif

The result is this fatal compilation error:

/usr/include/stdio.h:80: error: two or more data types in declaration
specifiers

This is with autoconf 2.63, Mac OS 10.5.6 PPC.

(Is there some reason why size_t need be defined to "unsigned int" rather 
than simply "unsigned"?)