RFR: 8238161: use os::fopen in HS code where possible

[Harold Seigel]

Please review this change to hotspot to call os::fopen() instead of fopen() so that the 'close-on-exec' flag gets set for these opened files.  This change was tested by running Mach5 tiers 1-2 on Linux, Mac OS, and Windows, and Mach5 tiers 3-5 on Linux x64.  Additionally, the changes were built on Linux PPC.

Thanks, Harold

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Commit messages:
 - 8238161: use os::fopen in HS code where possible

Changes: https://git.openjdk.java.net/jdk/pull/7022/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7022&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8238161
  Stats: 59 lines in 20 files changed: 1 ins; 0 del; 58 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7022.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7022/head:pull/7022

PR: https://git.openjdk.java.net/jdk/pull/7022