Add an option to silence all analyzer warnings.

People have been incorrectly using "-analyzer-disable-checker" to
silence analyzer warnings on a file, when analyzing a project. Add
the "-analyzer-disable-all-checks" option, which would allow the
suppression and suggest it as part of the error message for
"-analyzer-disable-checker". The idea here is to compose this with
"--analyze" so that users can selectively opt out specific files from
static analysis.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216763 91177308-0d34-0410-b5e6-96231b3b80d8