lang/pypy: update to 5.4.0

ChangeLog:

• Incremental improvements to cpyext (passing 99% of numpy's test suite)
• Update cffi to 1.8, supporting "limited API" mode for c-extensions on CPython >= 3.2
• Improved tooling for PyPy's JIT.
• Various new features, bug fixes and performance improvements, see: http://pypy.readthedocs.io/en/latest/release-pypy2.7-v5.4.0.html