[lit] Fix shtest-format external_shell failures

When using win32 cmd.exe, turn off command echoing at the beginning of
the script (@echo off).

Replace a bash shell script with a python script for the
fail_with_bad_encoding test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309399 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed