According to this report by the General Accounting Office,
there has been a lively trade in arms to China from both the
E.U. and the U.S. despite prohibitions against such trade
(though the report calls the amounts "small" -- over $300
million in the case of the U.S.).
The E.U. embargo does not have the force of law, although any
E.U. member nation faces the political consequences of defying
it. E.U. exports to China have included French submarines and
helicopters.
The U.S. embargo is law, but has provisions for waiver
by the Executive; such waivers have been allowed at least 11
times for satellite launches. And of course, the U.S. is
immune to global political consequences.
The embargoes were enacted after the 1989 crackdown on
dissidents in China's Tiananmen Square.
Recommended reading.