Improve GPT check and error expressiveness

Adds more GPT checks and more detailed error types to improve error
expressiveness.

Bug: 374792430

Change-Id: I35063e935cb93823b0b4772feedd933da18ccebf
6 files changed
tree: 0c2ed57afacb6c60a5891f64cf7cac582001bff7
  1. gbl/
  2. libxbc/
  3. vts/
  4. .clang-format
  5. .gitignore
  6. BUILD
  7. LICENSE
  8. OWNERS