os/signal: Factor call to sys::Sigaction into sys_sigaction internal helper

On MSVC we will need to use signal(2), because there is no sigaction,
and sigaction will be partly emulated through that. Move signal setting
code into common place as a preparatory step.

golang/os/signal.cpp

@@ -114,6 +114,8 @@ static void _notify(int signo);
 static void _checksig(int signo);
 static void _checkActEqual(const struct sigaction *a, const struct sigaction *b);
 static void _spinwaitNextQueueCycle();
+
+static int  sys_sigaction(int signo, const struct sigaction *act, struct sigaction *oldact);
 static void xsys_sigaction(int signo, const struct sigaction *act, struct sigaction *oldact);
 static void xsigemptyset(sigset_t *sa_mask);
 static bool _sigact_equal(const struct sigaction *a, const struct sigaction *b);
@@ -339,7 +341,7 @@ static int/*syserr*/ _Notify1(chan<os::Signal> ch, os::Signal sig) {
 
     // retrieve current signal action
     struct sigaction cur;
-    int syserr = sys::Sigaction(sig.signo, nil, &cur);
+    int syserr = sys_sigaction(sig.signo, nil, &cur);
     if (syserr < 0) {
         // TODO reenable once we can panic with any object
         //return fmt::errorf("sigaction sig%d: %w", sig.signo, sys::NewErrno(syserr);
@@ -385,7 +387,7 @@ static int/*syserr*/ _Notify1(chan<os::Signal> ch, os::Signal sig) {
 
         // register our sigaction
         struct sigaction old;
-        syserr = sys::Sigaction(sig.signo, &_actNotify, &old);
+        syserr = sys_sigaction(sig.signo, &_actNotify, &old);
         if (syserr < 0) {
             // TODO reenable once we can panic with any object
             //return fmt::errorf("sigaction sig%d: %w", sig.signo, sys::NewErrno(syserr);
@@ -465,7 +467,7 @@ static int/*syserr*/ _Ignore1(os::Signal sig) {
     if (h == nil) {
         h = new _SigHandler();
         h->sigstate.store(_SigIgnoring);
-        int syserr = sys::Sigaction(sig.signo, nil, &h->prev_act);
+        int syserr = sys_sigaction(sig.signo, nil, &h->prev_act);
         if (syserr < 0) {
             delete h;
             return syserr; // TODO errctx
@@ -477,7 +479,7 @@ static int/*syserr*/ _Ignore1(os::Signal sig) {
     h->sigstate.store(_SigIgnoring);
     h->subscribers.clear();
 
-    int syserr = sys::Sigaction(sig.signo, &_actIgnore, nil);
+    int syserr = sys_sigaction(sig.signo, &_actIgnore, nil);
     if (syserr < 0)
         return syserr; // TODO errctx
 
@@ -505,7 +507,7 @@ static int/*syserr*/ _Reset1(os::Signal sig) {
     h->sigstate.store(_SigReset);
 
     struct sigaction act;
-    int syserr = sys::Sigaction(sig.signo, &h->prev_act, &act);
+    int syserr = sys_sigaction(sig.signo, &h->prev_act, &act);
     if (syserr < 0)
         return syserr; // TODO errctx
     if (sigstate == _SigNotifying)
@@ -619,10 +621,13 @@ static void xsigemptyset(sigset_t *sa_mask) {
 }
 
 static void xsys_sigaction(int signo, const struct sigaction *act, struct sigaction *oldact) {
-    int syserr = sys::Sigaction(signo, act, oldact);
+    int syserr = sys_sigaction(signo, act, oldact);
     if (syserr != 0)
         panic("sigaction failed");   // TODO add errno detail
 }
+static int sys_sigaction(int signo, const struct sigaction *act, struct sigaction *oldact) {
+    return sys::Sigaction(signo, act, oldact);
+}
 
 static bool _sigact_equal(const struct sigaction *a, const struct sigaction *b) {
     // don't compare sigaction by memcmp - it will fail because struct sigaction