Corrected parser to avoid generation of multiple messages for a single error.
Summary of changes:
- Changed parser to eliminate generation of excessive error messages;
- Corrected lit tests to match all expected error messages;
- Corrected lit tests to guard against unwanted extra messages (added option "--implicit-check-not=error:");
- Added missing checks and fixed some typos in tests.
Note that changes in gfx8_asm_all.s, gfx9_asm_all.s and gfx10_asm_all.s are not shown because the files are too large.
See bug 46907