Fix compilation on sparc.
Patch from upstream, backported to the 11.0.0 release.

commit db785c7975e364acbf76a4db90296820d36b0740
Author: matoro <matoro@users.noreply.github.com>
Date:   Wed May 4 08:28:11 2022 -0400

    check for signal existence before registering in handler (#5)

    Some signals are only defined on certain platforms.  For example,
    SIGSTKFLT does not exist on sparc.  Use preprocessor macros to check for
    signal's existence before registering signal handler for it.

    Note that this is the same technique cpython uses:
    https://github.com/python/cpython/blob/3.10/Modules/signalmodule.c#L1427

    See: https://bugs.gentoo.org/807184

--- detachtty-11.0.0/attachtty.c
+++ detachtty-11.0.0/attachtty.c
@@ -94,8 +94,45 @@
 static void init_signal_handlers(void) {
     struct sigaction act;
     int i, fatal_sig[] = {
-        SIGHUP, SIGQUIT, SIGILL, SIGABRT, SIGBUS, SIGFPE, SIGSEGV, SIGPIPE,
-        SIGTERM, SIGSTKFLT, SIGCHLD, SIGXCPU, SIGXFSZ,
+#ifdef SIGHUP
+        SIGHUP,
+#endif
+#ifdef SIGQUIT
+        SIGQUIT,
+#endif
+#ifdef SIGILL
+        SIGILL,
+#endif
+#ifdef SIGABRT
+        SIGABRT,
+#endif
+#ifdef SIGBUS
+        SIGBUS,
+#endif
+#ifdef SIGFPE
+        SIGFPE,
+#endif
+#ifdef SIGSEGV
+        SIGSEGV,
+#endif
+#ifdef SIGPIPE
+        SIGPIPE,
+#endif
+#ifdef SIGTERM
+        SIGTERM,
+#endif
+#ifdef SIGSTKFLT
+        SIGSTKFLT,
+#endif
+#ifdef SIGCHLD
+        SIGCHLD,
+#endif
+#ifdef SIGXCPU
+        SIGXCPU,
+#endif
+#ifdef SIGXFSZ
+        SIGXFSZ,
+#endif
     };
     
     /* catch SIGINT and send character \003 over the link */
--- detachtty-11.0.0/detachtty.c
+++ detachtty-11.0.0/detachtty.c
@@ -392,9 +392,47 @@
 
 static void init_signal_handlers(void) {
     struct  sigaction act;
-    int i, fatal_sig[] = { SIGHUP, SIGQUIT, SIGILL, SIGABRT, SIGBUS, SIGFPE,
-                           SIGSEGV, /*SIGPIPE,*/ SIGTERM, SIGSTKFLT, SIGCHLD,
-                           SIGXCPU, SIGXFSZ, };
+    int i, fatal_sig[] = {
+#ifdef SIGHUP
+        SIGHUP,
+#endif
+#ifdef SIGQUIT
+        SIGQUIT,
+#endif
+#ifdef SIGILL
+        SIGILL,
+#endif
+#ifdef SIGABRT
+        SIGABRT,
+#endif
+#ifdef SIGBUS
+        SIGBUS,
+#endif
+#ifdef SIGFPE
+        SIGFPE,
+#endif
+#ifdef SIGSEGV
+        SIGSEGV,
+#endif
+#ifdef SIGPIPE
+        /*SIGPIPE,*/
+#endif
+#ifdef SIGTERM
+        SIGTERM,
+#endif
+#ifdef SIGSTKFLT
+        SIGSTKFLT,
+#endif
+#ifdef SIGCHLD
+        SIGCHLD,
+#endif
+#ifdef SIGXCPU
+        SIGXCPU,
+#endif
+#ifdef SIGXFSZ
+        SIGXFSZ,
+#endif
+    };
 
     /* catch SIGCHLD, SIGQUIT, SIGTERM, SIGILL, SIGFPE... and exit */
     act.sa_handler = fatal_signal_handler;