configure: Add --enable-clones for dynamic function multi-versioning.

configure.ac

@@ -266,6 +266,24 @@ AC_ARG_ENABLE(optimize, RB_HELP_STRING([--enable-optimize], [Enable optimization
 
 AM_CONDITIONAL([OPTIMIZE], [[[[ "$OPTIMIZE" = "1" ]]]])
 
+dnl
+dnl Enable target clones code generation
+dnl
+
+AC_MSG_CHECKING(whether to generate code for target clones)
+AC_ARG_ENABLE(clones, RB_HELP_STRING([--enable-clones], [Enable target clones generation]),
+[
+	AC_MSG_RESULT([yes])
+	AC_SUBST(CLONES, 1)
+	RB_DEFINE([CLONES], [1], [Function multi-versioning for different architectures])
+	clones="yes"
+], [
+	AC_MSG_RESULT([no])
+	clones="no"
+])
+
+AM_CONDITIONAL([CLONES], [[[[ "$CLONES" = "1" ]]]])
+
 dnl
 dnl Explicit link-time-optimization switch
 dnl
@@ -3154,6 +3172,7 @@ echo "Linker flags (LDFLAGS) ............ $LDFLAGS"
 echo
 echo "Developer platform (build) ........ $build_cpu $build_vendor $build_os"
 echo "Target platform (host) ............ $host_cpu $host_vendor $host_os"
+echo "Target clones ..................... $clones"
 echo "Target features ................... $machine_tuning $machine_features"
 echo
 echo "Precompile headers ................ $build_pch"

include/ircd/portable.h

@@ -81,6 +81,16 @@
 	#endif
 #endif
 
+//
+// Target clones
+//
+
+#ifdef RB_CLONES
+	#define IRCD_CLONES(features) gnu::target_clones(features)
+#else
+	#define IRCD_CLONES(features)
+#endif
+
 //
 // 128 bit integer support
 //