Merge changes Ibc7a9a94,I4e8a0683,I4f741262,Ib19c9666,Ib55dc8bd, ...
* changes:
header-checker: header-abi-dumper should use ModuleIR instead
header-checker: Extract common code to ModuleIR
header-checker: Remove getters from IRReader
header-checker: Fix minor style problem
header-checker: Do not expose format-specific details
header-checker: Rename to IRReader
header-checker: Split IRDumper and IRReader
header-checker: Extract ModuleIR
header-checker: Cleanup namespaces
header-checker: Restructure the source tree