Fix GCC 4.7 errors

GCC 4.7.2 fail overriding constructors defined with virtual and default.
Debian build also fails linking  without -lrt.
INT64_C is not defined on Debian with 4.7.2. "ll" should be enough.

Change-Id: Ia779f094ed64fc3b1941429485e81520d017c2f5
Reviewed-on: https://weave-review.googlesource.com/1671
Reviewed-by: Alex Vakulenko <avakulenko@google.com>
diff --git a/libweave_standalone.gyp b/libweave_standalone.gyp
index d6418db..d36d208 100644
--- a/libweave_standalone.gyp
+++ b/libweave_standalone.gyp
@@ -12,6 +12,7 @@
       '-lgmock',
       '-lgtest',
       '-lpthread',
+      '-lrt',
     ],
   },
   'targets': [