The canonical form splits a label from the instruction that follows it,
but an identifier naming a macro may expand into any token at all: moved
to a line of its own it no longer parses, because the parser accepts a
non-mnemonic first token only behind a label. The names #define'd in
the file now hold such content back, conservatively across the whole
file, and the crashing input joins the corpus.
Assisted-by: GLM 5.3
