`tkAs` was a member of two enums: TToolKind (uToolchain, ordinal 1) and
uLexer.TTokenKind (the lexer token enum, ordinal 40). In ResolveAssembler,
the bare assignment `Result.Kind := tkAs` should bind to TToolKind, but
bare-member resolution is cross-unit order-fragile and could bind it to
TTokenKind.tkAs (ordinal 40) instead. 40 is out of range for the 4-member
TToolKind, so any downstream code that switches or indexes on the resolved
Kind runs off the end into a wild pointer — a layout-sensitive crash that
manifested intermittently in the test runner (a metaclass typeinfo symbol
truncation surfacing as a SIGSEGV during teardown).
Renaming the member to tkGnuAs removes the ambiguity entirely: `tkAs` now
exists only in uLexer.TTokenKind. This is bootstrap-safe (no qualified-enum
syntax, which the release binary does not yet support). Verified the
ResolveAssembler codegen now bakes Ord(tkGnuAs)=1 (was 40).
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