[runtime] Use getprotobyname_r() where needed and available

Fixes mono#7087

configure.ac

@@ -2286,6 +2286,23 @@ if test x$host_win32 = xno; then
 		AC_MSG_RESULT(no)
 	])
 
+	dnl **********************************
+	dnl *** Check for getprotobyname_r ***
+	dnl **********************************
+	AC_MSG_CHECKING(for getprotobyname_r)
+		AC_TRY_LINK([
+		#include <stdio.h>
+		#include <netdb.h>
+	], [
+		getprotobyname_r(NULL, NULL, NULL, 0, NULL);
+	], [
+		# Yes, we have it...
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_GETPROTOBYNAME_R, 1, [Have getprotobyname_r])
+	], [
+		AC_MSG_RESULT(no)
+	])
+
 	dnl **********************************
 	dnl *** Check for getnameinfo ***
 	dnl **********************************

mono/utils/networking-posix.c

@@ -127,7 +127,24 @@ mono_get_address_info (const char *hostname, int port, int flags, MonoAddressInf
 
 #endif
 
-#ifdef HAVE_GETPROTOBYNAME
+#if (defined(__linux__) && defined (HAVE_GETPROTOBYNAME_R)
+
+static int
+fetch_protocol (const char *proto_name, int *cache, int *proto, int default_val)
+{
+	if (!*cache) {
+		struct protoent protoent_buf = { 0 };
+		struct protoent *pent = NULL;
+		char buf[1024];
+
+		getprotobyname_r (proto_name, &protoent_buf, buf, 1024, &pent);
+		*proto = pent ? pent->p_proto : default_val;
+		*cache = 1;
+	}
+	return *proto;
+}
+
+#elif HAVE_GETPROTOBYNAME
 
 static int
 fetch_protocol (const char *proto_name, int *cache, int *proto, int default_val)
@@ -142,6 +159,8 @@ fetch_protocol (const char *proto_name, int *cache, int *proto, int default_val)
 	return *proto;
 }
 
+#endif
+
 int
 mono_networking_get_tcp_protocol (void)
 {
@@ -163,8 +182,6 @@ mono_networking_get_ipv6_protocol (void)
 	return fetch_protocol ("ipv6", &cache, &proto, 41); //41 is SOL_IPV6 on linux
 }
 
-#endif
-
 #if defined (HAVE_SIOCGIFCONF)
 
 #define IFCONF_BUFF_SIZE 1024