bpo-45163: Haiku build fix. (pythonGH-28269)

linkage issues mainly for shared libs and missing system library,
also little nit into the signal extension as strsignal returns
a constant in this platform.

Author: devnexen

Misc/NEWS.d/next/Build/2021-09-11-06-05-23.bpo-45163.q7xT93.rst

@@ -0,0 +1 @@
+Fixes Haiku platform build.

Modules/signalmodule.c

@@ -611,7 +611,7 @@ static PyObject *
 signal_strsignal_impl(PyObject *module, int signalnum)
 /*[clinic end generated code: output=44e12e1e3b666261 input=b77914b03f856c74]*/
 {
-    char *res;
+    const char *res;
 
     if (signalnum < 1 || signalnum >= NSIG) {
         PyErr_SetString(PyExc_ValueError,

configure.ac

@@ -2736,7 +2736,7 @@ then
 			BLDSHARED="$LDSHARED"
 		fi
 		;;
-	Linux*|GNU*|QNX*|VxWorks*)
+	Linux*|GNU*|QNX*|VxWorks*|Haiku*)
 		LDSHARED='$(CC) -shared'
 		LDCXXSHARED='$(CXX) -shared';;
 	FreeBSD*)
@@ -2805,6 +2805,7 @@ then
 	Linux-android*) ;;
 	Linux*|GNU*) CCSHARED="-fPIC";;
 	FreeBSD*|NetBSD*|OpenBSD*|DragonFly*) CCSHARED="-fPIC";;
+	Haiku*) CCSHARED="-fPIC";;
 	OpenUNIX*|UnixWare*)
 		if test "$GCC" = "yes"
 		then CCSHARED="-fPIC"
@@ -3098,6 +3099,9 @@ AC_SUBST(TZPATH)
 AC_CHECK_LIB(nsl, t_open, [LIBS="-lnsl $LIBS"]) # SVR4
 AC_CHECK_LIB(socket, socket, [LIBS="-lsocket $LIBS"], [], $LIBS) # SVR4 sockets
 
+# Haiku system library
+AC_CHECK_LIB(network, socket, [LIBS="-lnetwork $LIBS"], [], $LIBS)
+
 AC_MSG_CHECKING(for --with-libs)
 AC_ARG_WITH(libs,
             AS_HELP_STRING([--with-libs='lib1 ...'], [link against additional libs (default is no)]),