+        dnl
+        dnl the tests here are based on ACX_PTHREAD macro from autoconf macro
+        dnl archive from http://ac-archive.sourceforge.net/
+        dnl
+        dnl thanks to Steven G. Johnson <stevenj@alum.mit.edu> and Alejandro
+        dnl Forero Cuervo <bachue@bachue.com> for the original code
+
+        dnl TODO: cache the result
+
+        dnl define the list of the thread options to try in the loop below
+        dnl with the convention that anything starting with '-' is a cpp flag
+        dnl while anything else is a library (i.e. there is an implicit "-l")
+        THREAD_OPTS="-pthread"
+        case "${host}" in
+          *-*-solaris2* | *-*-sunos4* )
+                if test "x$GCC" = "xyes"; then
+                    dnl apparently some Solaris/gcc combinations use this one
+                    THREAD_OPTS="$THREAD_OPTS -pthreads"
+                else
+                    THREAD_OPTS="-mt $THREAD_OPTS"
+                fi
+                ;;
+          *-*-freebsd*)
+                dnl look, in order, for the kernel threads, then Linux threads
+                dnl and finally the userland threads
+                THREAD_OPTS="-kthread lthread $THREAD_OPTS c_r"
+                ;;
+          *-*-aix* )
+                dnl AIX calls the library libpthreads - thanks IBM!
+                THREAD_OPTS="pthreads"
+                ;;
+          *)
+                dnl the default is ok but if it doesn't work try without it
+                dnl just in case
+                THREAD_OPTS="$THREAD_OPTS none"
+        esac