SQLite uses GNU configure on Unixish platforms to look for various
system calls and headers.  If newer calls exist then SQLite uses them,
otherwise it uses various workarounds, emulations, or omits calls to
them.

Examples of things looked for are usleep, fdatasync, re-entrant time
functions.

To avoid polluting the parent directory with all the configure related
files they are in this subdirectory.  The files have been copied
unaltered from the SQLite amalgamation.