RFR: JDK-8295710 : unify os::dll_file_extension [v3]

[Matthias Baesken]

> The os::dll_file_extension() function could be unified for the different OS platforms.

Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:

  remove dll_file_extension from os.hpp

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10782/files
  - new: https://git.openjdk.org/jdk/pull/10782/files/76a230e9..56495228

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10782&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10782&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10782.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10782/head:pull/10782

PR: https://git.openjdk.org/jdk/pull/10782