Support @Version and @Line as built-in symbols. For now, resolves @Version to 1427 (the same as for the VS 2019 release of ML.EXE).
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D104964
MASM specifies that all variable definitions are redefinable, except for EQU definitions to expressions. (TEXTEQU is unspecified, but appears to be fully redefinable as well.)
Also, in practice, ML.EXE allows redefinitions where the value doesn't change.
Make variable redefinition possible for text macros, suppressing expansion if written as the first argument to an EQU or TEXTEQU directive.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D103993
Eric Astor