[libcxx] Fixed a number of typos

[libcxx] Fixed a number of typos

I went over the output of the following mess of a command:

`(ulimit -m 2000000; ulimit -v 2000000; git ls-files -z | parallel --xargs -0 cat | aspell list --mode=none --ignore-case | grep -E '^[A-Za-z][a-z]*$' | sort | uniq -c | sort -n | grep -vE '.{25}' | aspell pipe -W3 | grep : | cut -d' ' -f2 | less)`

and proceeded to spend a few days looking at it to find probable typos
and fixed a few hundred of them in all of the llvm project (note, the
ones I found are not anywhere near all of them, but it seems like a
good start).

Reviewed By: #libc, philnik

Spies: philnik, libcxx-commits, mgorny, arichardson

Differential Revision: https://reviews.llvm.org/D130905