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This ports the abseil .def file generation to Windows, using dumpbin to
get the lists of symbols. It also fixes some glitches such as the
Chromium-repo detection, and file-endings on export. It works around one
dumpbin bug that will be fixed in some future VS release.

The results are not identical to those on Linux but this is a solid step
in that direction.

Bug: 1046390
Change-Id: I37e7055b9b774e4d923e5572dd00268b0d563c53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264493Reviewed-by: Danil Chapovalov <danilchap@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804437}