ELF: Rewrite "echo" command arguments in hope that would fix a test breakage.

Previously, we used both single quotes and double quotes, and
some single-quoted tokens are concatenated with next tokens because
there were no spaces between them. That may be a cause of test flakiness
on Windows, which is reported as https://llvm.org/bugs/show_bug.cgi?id=26388.

The new test commands are more straightforward than before.

llvm-svn: 259559