include -pthread in LDFLAGS and not LIBS as the latter doesn't appear in wx-config output unless --static is given

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@17196 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

configure.in

@@ -3358,7 +3358,8 @@ if test "$TOOLKIT" != "MSW"; then
       else
           dnl yes, these special compiler flags should be used with the
           dnl linker as well
-          LIBS="$THREADS_LINK $THREADS_CFLAGS $LIBS"
+          LDFLAGS="$THREADS_CFLAGS $LDFLAGS"
+          LIBS="$THREADS_LINK $LIBS"
 
           AC_MSG_CHECKING([if more special flags are required for pthreads])
           flag=no