feat(driver): color diagnostics like gcc with -fdiagnostics-color

Add -fdiagnostics-color[=auto|always|never] and -fno-diagnostics-color.
The default auto mode colors only a terminal stderr (TERM set and not
dumb on Unix; a console that accepts VT sequences on Windows), so test
harnesses, the desktop bundle and other pipes stay plain.

Every diagnostic label now comes from cps::diagnosticPrefix, which emits
gcc's default GCC_COLORS bytes: bold locus, bold red error/fatal error,
bold magenta warning, bold cyan note. compilation terminated., runtime
messages of the compiled program and lld output are unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions