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

[Harold Seigel]

On Mon, 10 Jan 2022 21:02:54 GMT, Harold Seigel <hseigel at openjdk.org> wrote:

> 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

Thanks Matthias and Coleen for reviewing this!

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