RFR: 8286431: Do not use resource array in posix mmap_attach_shared()

[Ioi Lam]

Please review this small clean up

perfMemory_posix.cpp uses a lot of explicit C heap alloc/free because the function may be called during early VM bootstrap, before ResourceMark can be used.

However, we have a single odd use of resource allocation in this file. It's supposed to work with Java exceptions. However, the code actually makes an explicitly exception check, so there's no need to do the resource alloc at all.

Also, there's no need to close the fd in case of exception.

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Commit messages:
 - 8286431: Do not use resource array in posix mmap_attach_shared()

Changes: https://git.openjdk.org/jdk/pull/10686/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10686&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286431
  Stats: 18 lines in 1 file changed: 1 ins; 13 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10686.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10686/head:pull/10686

PR: https://git.openjdk.org/jdk/pull/10686