configure.in: cross-compile

[Dengke Du]

Hi all

When apr used in cross-compile, it pass 8 bytes to ac_cv_sizeof_off_t by 
the following:

    APR_CHECK_SIZEOF_EXTENDED([#include <sys/types.h>], off_t, 8)

at the line 1789 in configure.in

But when the target is x86, the apr configure as "off_t = 8", but in 
glibc the size of off_t is 4, so it maybe error, when we use the apr.h,

such as subversion.

// Dengke