RFR: 7903837: apidiff: build.sh issues on Windows

Wed Sep 25 17:57:15 UTC 2024

Please review some `build.sh` and `Makefile` changes to address issues building on Windows.

The primary Windows issue was missing use of `mixed_path` when passing some filenames into `make`.
There is some additional cleanup (for all platforms) to normalize the `DEPS_DIR` and add missing items to the `sanity` and `check_build_vars` targets.

This has been tested on macOS. Can someone with access to a Windows machine test it on Windows, please?

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Commit messages:
 - CODETOOLS-7903837: apidiff: build.sh issues on Windows

Changes: https://git.openjdk.org/apidiff/pull/12/files
  Webrev: https://webrevs.openjdk.org/?repo=apidiff&pr=12&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903837
  Stats: 33 lines in 3 files changed: 13 ins; 3 del; 17 mod
  Patch: https://git.openjdk.org/apidiff/pull/12.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/12/head:pull/12

PR: https://git.openjdk.org/apidiff/pull/12