Currently, a pragma AST node's recorded location starts at the
namespace token (such as `omp` in the case of OpenMP) after the
`#pragma` token, and the `#pragma` location isn't available. However,
the `#pragma` location can be useful when, for example, rewriting a
directive using Clang's Rewrite facility.
This patch makes `#pragma` locations available in any `PragmaHandler`
but it doesn't yet make use of them.
This patch also uses the new `struct PragmaIntroducer` to simplify
`Preprocessor::HandlePragmaDirective`. It doesn't do the same for
`PPCallbacks::PragmaDirective` because that changes the API documented
in `clang-tools-extra/docs/pp-trace.rst`, and I'm not sure about
backward compatibility guarantees there.
Reviewed By: ABataev, lebedev.ri, aaron.ballman
Differential Revision: https://reviews.llvm.org/D61643
llvm-svn: 361335
ddde0ec1e4