Revert "722200 - configure script does not pick the correct am_cv_scanf version"

This reverts commit f3e76fb9df0c4b1276909a8f33421ee6c79f5455.
Revert "722200 - configure script does not pick the correct am_cv_scanf version"

This reverts commit f9548652de6b0684d818bc5bd147942453dd8886.
722200 - configure script does not pick the correct am_cv_scanf version

Different tack: Use G_GUINT64_FORMAT in guid.c instead of messing with
defining __USE_MINGW_ANSI_STDIO
Fix broken win32 build; MinGW needs our strptime.