build: Compile with -ftrapv.

This causes signed overflow to raise an exception. The option is
supported on the lowest gcc version we support, so we don't bother
to check by calling cc-option() in Makefile.real.

diff --git a/Makefile.real b/Makefile.real
index 6e8084d542b8888e2a838671b6a9be845ac2cae2..9a6c7e76fe1e9d95d4634e3298ce660b69366e9f 100644 (file)
--- a/Makefile.real
+++ b/Makefile.real
@@ -119,6 +119,7 @@ CPPFLAGS += -I$(yy_build_dir)
 CPPFLAGS += $(lopsub_cppflags)
 
 STRICT_CFLAGS += -fno-strict-aliasing
+STRICT_CFLAGS += -ftrapv
 STRICT_CFLAGS += -g
 STRICT_CFLAGS += -Os
 STRICT_CFLAGS += -Wundef -W -Wuninitialized