Merge ModuleIR within single thread

This commit moves the ModuleMerger::MergeGraphs function calls from the
reader threads to the main thread. The dumps are merged to the final
ModuleIR in a deterministic order.

Test: development/vndk/tools/header-checker/tests/test.py
Bug: 162201277
Change-Id: I9f6ea5bcbef0c74ff4c87b825bfec5ef02575ab2
1 file changed