GDB builders will not be failed by build/lit-test failures

These mails are getting annoying to myself (& probably Eric) and don't
add a lot of value to other users either (actual Clang/LLVM
build/lit-test verification is done by any number of other machines and
doesn't need to be reported by the GDB builders)

Also rename the gdb/gcc svn checkout tasks to be more
specific/descriptive.

git-svn-id: https://llvm.org/svn/llvm-project/zorg/trunk@197749 91177308-0d34-0410-b5e6-96231b3b80d8