Diagnostic categories are entirely unused and arguably useless as
implemented, as they merely denote the sub-component of the
compiler.
As far as categorizing warnings are concerned, I'm abandoning the
effort for now, as the utility is marginal and Swift and the Swift
compiler are probalby not ready for these to be nailed down. For the
sake of cleanliness, the CATEGORY field is also stripped from
WARNINGS.
If there's a need for automatic identifying of compiler sub-components
for diagnstics in the future, there are better ways to do this.
NFC
Added DiagnosticsDriver.def and DiagnosticsDriver.h for driver-only diagnostics.
(Diagnostics which are shared with the frontend remain in
DiagnosticsFrontend.{def,h}.)
Added a DiagnosticEngine& to Compilation, so that it can emit diagnostics for
events which occur while performing Jobs.
Replaced all of the locations where we were manually printing error messages to
emitting real diagnostics, adding diagnostics if necessary.
Updated Driver::buildCompilation() so that it fails early if any errors were
encountered.
Updated test/Driver/actions.swift to pass a -module-name for multi-input tests.
Swift SVN r13175
