Add xptr_locs flag to win32/configure.js

The xptr_locs flag was added in commit 67070107 but no flag was added to
win32/configure.js, leading a compile error I had on windows where the
@WITH_XPTR_LOCS@ macro was not replaced properly on windows.
7 jobs for xptrlocs in 8 minutes and 9 seconds (queued for 1 second)