RFR: 8294594: Fix cast-function-type warnings in signal handling code [v2]

[Aleksey Shipilev]

> After [JDK-8294314](https://bugs.openjdk.org/browse/JDK-8294314), we would have signals_posix.cpp excluded with cast-function-type warning:

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Naming
 - Redo using the proper signatures
 - Merge branch 'master' into JDK-8294594-warning-cast-function-type-signals
 - Fix

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10494/files
  - new: https://git.openjdk.org/jdk/pull/10494/files/2ca21e2a..c469e840

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10494&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10494&range=00-01

  Stats: 14704 lines in 421 files changed: 10039 ins; 3141 del; 1524 mod
  Patch: https://git.openjdk.org/jdk/pull/10494.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10494/head:pull/10494

PR: https://git.openjdk.org/jdk/pull/10494