gcc 4.6 doesn't have the -std=c++11 option, it uses the not-yet-finalized
-std=c++0x option. Use whichever is found to be appropriate at configure
time.
The latest versions of v8 build libicu as well. If this isn't copied to
the lib directory, then the v8 version check fails (with a link error).
Ensure that this is caught at configuration time.
If you don't want to overwrite the system copy of v8 in /usr/lib/libv8.so,
you can use the --with-v8=<path> option to have php-v8js use its own
copy of libv8.
Note that threads are implemented using std::thread which is only available in C++0x. The relevant compile flags have been added but compiler support has not been tested and is therefore not guaranteed.