Bug #924585: configure fails on Ubuntu 11.10

Fixed a problem with pthread_once() not being detected by configure on
modern distributions.

configure.ac

@@ -259,6 +259,11 @@ AC_CHECK_DECL([clock_gettime],
 )
 AC_SEARCH_LIBS([clock_gettime], [rt]) 
 
+save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+save_LIBS="$LIBS"
+LIBS="$PTHREAD_LIBS $LIBS"
+
 AC_CHECK_FUNCS([ \
 alarm \
 directio \
@@ -283,6 +288,9 @@ AC_CHECK_FUNC(pthread_once, ,
               AC_MSG_ERROR([*** pthread_once() is not available on this platform ***])
 )
 
+LIBS="$save_LIBS"
+CFLAGS="$save_CFLAGS"
+
 AC_ARG_WITH([debug],
     [AS_HELP_STRING([--with-debug],
        [Add debug code/turns off optimizations (yes|no) @<:@default=no@:>@])],