Bug ID: JDK-8294594 Fix cast-function-type warnings in signal handling code

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JDK 20
20Unresolved

After JDK-8294314, we would have signals_posix.cpp excluded with cast-function-type warning:

```
/home/shade/trunks/jdk/src/hotspot/os/posix/signals_posix.cpp: In function 'int SR_initialize()':
/home/shade/trunks/jdk/src/hotspot/os/posix/signals_posix.cpp:1727:20: error: cast between incompatible function types from 'void (*)(int, siginfo_t*, ucontext_t*)' to 'void (*)(int)' [-Werror=cast-function-type]
 1727 |   act.sa_handler = (void (*)(int)) SR_handler;
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~
```

A closer look would reveal that we are using the wrong slots for SR_handler, `sa_handler` vs `sig_handler`, which manifests in type cast errors. `man sigaction` says:

```
       If SA_SIGINFO is specified in sa_flags, then sa_sigaction (instead  of  sa_handler)  specifies  the  signal-handling
       function for signum.  This function receives three arguments, as described below.
```