Driver: Quote the command in crash reproduction scripts.

This fixes crash report generation when filenames have spaces. It also
removes an awkward workaround that quoted *some* arguments when
generating crash reports.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@220307 91177308-0d34-0410-b5e6-96231b3b80d8