Spell out the units used for the `offset` argument, so that people do
not try to scale to units of bytes themselves.
auto merge of #11002 : pnkfelix/rust/fsk-improve-doc-for-ptr-offset, r=alexcrichton

Spell out the units used for the `offset` argument, so that people do not try to scale to units of bytes themselves.
llvm: Disable pthread on mingw

llvm supports both win32 native threads and pthread,
but configure tries to find pthread first.
This manually disables pthread to use native api.

This removes libpthreads-2.dll dependency on librustc.