[lit] Support parsing scripts with inconsistent or invalid encodings.

 - For whatever reason, we have a lot of test files with bogus unicode
   characters. This patch allows those scripts to still be parsed on Python3 by
   changing the parsing logic to work on binary files, and only require the
   actual script commands to be convertible to ascii.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188376 91177308-0d34-0410-b5e6-96231b3b80d8
Add the C99 hex-float assembly syntax to our extension document.

As Ben pointed out, GAS doesn't support this syntax so we should give at least
some warning that it might not be portable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188377 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r188376, "[lit] Support parsing scripts with inconsistent or invalid encodings.", this doesn't work yet for bots using the internal shell.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188379 91177308-0d34-0410-b5e6-96231b3b80d8