[dev.cc] cmd/asm: fix macro definition bug in the lexer
Because text/scanner hides the spaces, the lexer treated
#define A(x)
and
#define A (x)
the same, but they are not: the first is an argument with macros, the
second is a simple one-word macro whose definition contains parentheses.
Fix this by noticing the relative column number as we move from A to (.
Hacky but simple.
Also add a helper to recognize the peculiar ARM shifted register operators.