2b11c7de4a introduced
`llvm/include/llvm/MC/MCAsmLexer.h` and made `AsmLexer` inherit from
`MCAsmLexer`, likely to allow target-specific parsers to depend solely
on `MCAsmLexer`. However, this separation now seems unnecessary and
confusing.
`MCAsmLexer` defines virtual functions with `AsmLexer` as its only
implementation, and `AsmLexer` itself has few extra public methods.
To simplify the codebase, this change merges MCAsmLexer.{h,cpp} into
AsmLexer.{h,cpp}. MCAsmLexer.h is temporarily kept as a forwarder.
Note: I doubt that a downstream lexer handling an assembly syntax
significantly different from the standard GNU Assembler syntax would
want to inherit from `MCAsmLexer`. Instead, it's more likely they'd
extend `AsmLexer` by adding new states and modifying its internal logic,
as seen with variables for MASM, M68k, and HLASM.
c9f6d26e04