Accept name filters and exclusions in --export

[ASDAlexander77]

Summary

• --export is now a comma-separated list instead of the all/none enum. Existing --export=all and --export=none behave as before.
• A name exports that declaration even without the export keyword. It matches the short or namespaced name (add, M.add) and accepts globs (M.*).
• !name excludes a name and always wins over an including filter. With only exclusions (--export=!sub) the export keyword decides, minus the excluded names.
• Class and interface members are filtered by their owner's name. Each variable of one export let a, b statement is decided on its own.
• The rules live in MLIRExportFilter.h (isExportedByFilters), used by getExportModifier.

Example: --export=M.*,!M.internal*,!M.b

Note: in bash, quote values containing ! ('--export=!sub').

Test plan

• New ExportFilterTest unit tests (7) pass; MLIRGenTests 66/66
• All 268 shared-library ctest tests pass
• DLL export tables checked with llvm-objdump -p for no option, none, M.add,sub, !sub and M.*,!M.internal*,!M.b: each exports exactly the expected symbols, including per-variable filtering of export let a = 1, b = 2
• Known, not changed here: --export=all on a DLL that uses the default lib fails to link (LNK1242, a default-lib generic instantiation gets an invalid export name). A compiler built before this change fails the same way.

🤖 Generated with Claude Code