Merge pull request #1009 from sgraham/fix-null.o

Don't output null.o during configure
diff --git a/configure.py b/configure.py
index b8d7096..64f940b 100755
--- a/configure.py
+++ b/configure.py
@@ -325,7 +325,8 @@
         cflags += ['-O2', '-DNDEBUG']
     try:
         proc = subprocess.Popen(
-            [CXX, '-fdiagnostics-color', '-c', '-x', 'c++', '/dev/null'],
+            [CXX, '-fdiagnostics-color', '-c', '-x', 'c++', '/dev/null',
+             '-o', '/dev/null'],
             stdout=open(os.devnull, 'wb'), stderr=subprocess.STDOUT)
         if proc.wait() == 0:
             cflags += ['-fdiagnostics-color']