flow: only enable LEC_CHECK when kepler-formal is installed

kepler-formal is primarily an OpenROAD/ORFS developer tool. End-users
would typically run LEC transactionally at project completion, not in
every CI run. Default LEC_CHECK to 0 when kepler-formal is not present
to avoid hard failures in environments where it is not installed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

flow/settings.mk

@@ -1 +1,5 @@
-export LEC_CHECK ?= 1
+# Enable LEC (Logical Equivalence Check) only if kepler-formal is installed.
+# kepler-formal is primarily an OpenROAD/ORFS developer tool, not an end-user
+# tool. End-users would typically run LEC transactionally at project completion,
+# not in every CI run where it wastes CI time.
+export LEC_CHECK ?= $(if $(wildcard $(KEPLER_FORMAL_EXE)),1,0)