target/hppa: Fix FPE exceptions

target/hppa: Fix FPE exceptions

Implement FP exception register #1 (lower 32-bits of 64-bit fr[0]).
A proper implementation is necessary to allow the Linux kernel in
system mode and the qemu linux-user to send proper si_code values
on SIGFPE signal.

Always set the T-bit on taken exception, and merge over- and underflow
in system mode to just set overflow bit to mimic the behaviour I tested
on a physical machine.

The test program below can be used to verify correct behaviour. Note
that behaviour on SIGFPE may vary on different platforms. The program
should always detect the correct signal, but it may or may not be able
to sucessfully continue afterwards.

 #define _GNU_SOURCE
 #include <signal.h>
 #include <stdio.h>
 #include <fenv.h>
 #include <float.h>

 static void fpe_func(int sig, siginfo_t *i, void *v) {
    sigset_t set;
    sigemptyset(&set);
    sigaddset(&set, SIGFPE);
    sigprocmask(SIG_UNBLOCK, &set, NULL);
    printf("GOT signal %d with si_code %ld\n", sig, i->si_code);
 }

 int main(int argc, char *argv[]) {
    struct sigaction action = {
        .sa_sigaction = fpe_func,
        .sa_flags = SA_RESTART|SA_SIGINFO };
    sigaction(SIGFPE, &action, 0);
    feenableexcept(FE_OVERFLOW | FE_UNDERFLOW);
    double x = DBL_MIN;
    return printf("%lf\n", argc > 1
        ? 1.7976931348623158E308*1.7976931348623158E308
        : x / 10);
 }

Signed-off-by: Helge Deller <deller@gmx.de>
(cherry picked from commit ebd394948de4e868cb8fc5b265a8a18f0935dce1)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>