RFR: 8261939: os::strdup_check_oom() should be used in os::same_files() in os_windows.cpp

[Calvin Cheung]

This to to address a review comment for JDK-8202750: 
https://github.com/openjdk/jdk/pull/2581#discussion_r577984793

I forgot to push this change before integration for JDK-8202750.

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Commit messages:
 - 8261939 (initial commit)

Changes: https://git.openjdk.java.net/jdk/pull/2621/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2621&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261939
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2621.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2621/head:pull/2621

PR: https://git.openjdk.java.net/jdk/pull/2621