Un-xfail test for 7385

I've verified that it works on osx x86_64

Closes #7385
Fix minor doc typos
Add test case for issue 7911
bump minimum supported OS X version to 10.7

Closes #11927
Closes #10842
Closes #2024
mark Windows 8 as supported
mark the minimum supported Linux kernel version

This is just taken from the binary itself. It would be nice to mark the
minimum glibc version too, and the corresponding RHEL/CentOS version.
Add test cases for #4063.

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>
Add test for sensible #[start] error message.

Fixes #9575.
Remove the obsolete handler for `impl A;`.

This is has been obsolete for quite a while now (including a release),
so removing the special handling seems fine. (The error message is quite
good still anyway.)

Fixes #9580.
Test for null buffer in CString.len()/.iter() and fail

Also change .as_str() to fail on null buffer.
Remove the need to count lang items

This solves horrible diffs where all you do is renumber literally everything.