Driver: When printing a "command was signalled" type of diagnostic, use the

Driver: When printing a "command was signalled" type of diagnostic, use the
short name of the tool in use, instead of the name of the action that created
the command. The practical impact is we now get:
  clang: error: clang frontend command failed due to signal 6 (use -v to see invocation)
instead of:
  clang: error: assembler command failed due to signal 6 (use -v to see invocation)
when clang crashes on a job that uses the integrated assembler.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@104417 91177308-0d34-0410-b5e6-96231b3b80d8