[master] fix src/lib/util/threads compiler/linker flags

This fixes the compilation issue shown on http://git.bind10.isc.org/~tester/builder/BIND10-valgrind/20121003092419-CentOS5-x86_64-GCC/logs/build.out

Discussed on jabber

src/lib/util/threads/Makefile.am

@@ -2,7 +2,7 @@ SUBDIRS = . tests
 AM_CXXFLAGS = $(B10_CXXFLAGS)
 
 AM_CPPFLAGS = -I$(top_srcdir)/src/lib -I$(top_builddir)/src/lib
-AM_CPPFLAGS += $(BOOST_INCLUDES)
+AM_CPPFLAGS += $(BOOST_INCLUDES) $(MULTITHREADING_FLAG)
 
 lib_LTLIBRARIES = libb10-threads.la
 libb10_threads_la_SOURCES  = lock.h lock.cc

src/lib/util/threads/tests/Makefile.am

@@ -1,7 +1,7 @@
 SUBDIRS = .
 
 AM_CPPFLAGS = -I$(top_builddir)/src/lib -I$(top_srcdir)/src/lib
-AM_CPPFLAGS += $(BOOST_INCLUDES)
+AM_CPPFLAGS += $(BOOST_INCLUDES) $(MULTITHREADING_FLAG)
 # XXX: we'll pollute the top builddir for creating a temporary test file
 # # used to bind a UNIX domain socket so we can minimize the risk of exceeding
 # # the limit of file name path size.
@@ -25,7 +25,7 @@ run_unittests_SOURCES += thread_unittest.cc
 run_unittests_SOURCES += lock_unittest.cc
 
 run_unittests_CPPFLAGS = $(AM_CPPFLAGS) $(GTEST_INCLUDES)
-run_unittests_LDFLAGS = $(AM_LDFLAGS) $(GTEST_LDFLAGS)
+run_unittests_LDFLAGS = $(AM_LDFLAGS) $(GTEST_LDFLAGS) $(PTHREAD_LDFLAGS)
 
 run_unittests_LDADD = $(top_builddir)/src/lib/util/threads/libb10-threads.la
 run_unittests_LDADD += \