Remove stale comment
Create the clang::DiagnosticConsumer for error reporting by ourselves

It's still one that just prints to the console, but now we can replace
it with our own implementation

The diagnostic options end up slightly different from those in the
internal clang instance, but they're close enough. However, one test
required relaxing a warning check a bit because of this.
Disable fixit hints printing

We don't generate them, and we won't forward the clang-generated ones to
the API
Replace clang diag client with our own, which does mostly the same

But can be changed to split the work between the lib and CLI tool by
exposing the info through the API
Collect formatted log messages in lib, print in cli validator

Unfortunately Clang prints some messages directly to stderr without
using the diagnostics system, so they get reordered before the messages
we are able to collect, and are not available to lib API users
WebCLDiag: Collect source snippets relevant to diagnostics, print in driver
Disable file:line:col printing in diagnostics

It refers to a temp file which will be gone by the time somebody reads
them, and locations which don't match the original source, so it's
useless

To be reinstated once we can map transformed source lines to original
source (if ever)
Print diag msg level in driver, stop using clang::TextDiagnostic
WebCLDiag: Remove now-useless diagOpts

The diagnostic client is now completely self-contained and doesn't use
any Clang APIs which take DiagnosticOptions, so this is no longer needed
WebCLDiag: Don't store LangOptions/Preprocessor

They're not needed anymore
Merge pull request #80 from ollisal/diagnostics

Collect warnings/errors into "validation log", expose through libclv API, print in driver