http://bugs.gentoo.org/show_bug.cgi?id=307159

E.g. on Solaris you can't just do -lpthread, even though you can find
symbols there.  In general, GCC knows best how to properly do it, so let
it do it for us, instead of relying on our own deviced logic.

--- configure.in
+++ configure.in
@@ -1018,10 +1018,14 @@
 	AC_DEFINE(_REENTRANT)
 	AC_DEFINE(_THREAD_SAFE)
 	AC_DEFINE(HAVE_LIBPTHREAD)
-	case $pthread_lib in
-	c)
+	case $pthread_lib::$GCC in
+	*::yes)
+		# GCC knows best, let it handle it
+		LIBS="-pthread $LIBS"
+		;;
+	c::*)
 	    ;;
-	c_r)
+	c_r::*)
 	    MAINLIBS="-pthread $MAINLIBS"
 	    ;;
 	*)