Added libstd and libextra unit tests to check-fast target.
Fixed MemoryMap on Windows.
Disabled failing parts of abs_sub() and frexp() unit tests on Windows.
Turned off libstd unit tests that currently fail on Windows.
auto merge of #8819 : vadimcn/rust/unit-tests, r=brson

Some of the tests are failing.  I've only managed to fix 'memory_map_file', the rest are up for grabs...

Fixes #5261.