[bcanalyzer] Recognize more stream types

Summary:
`llvm-bcanalyzer` prints out the stream type of the file it is
analyzing. If the file begins with the LLVM IR magic number, it reports
a stream type of "LLVM IR". However, any other bitstream format is
reported as "unknown".

Add some checks for two other common bitstream formats: Clang AST
files, which begin with 'CPCH', and Clang serialized diagnostics, which
begin with 'DIAG'.

Test Plan: `check-llvm`

Reviewers: pcc, aprantl, mehdi_amini, davide, george.karpenkov, JDevlieghere

Reviewed By: JDevlieghere

Subscribers: JDevlieghere, bruno, davide, llvm-commits

Differential Revision: https://reviews.llvm.org/D41979

llvm-svn: 330529

0 files changed, 0 insertions, 0 deletions