hints/linux.370: Add support for ubsan (undefined behaviour sanitizer) for gcc

This will add an option to compile and link nethack executable
with ubsan and catch undefined behaviour errors on runtime.

sys/unix/hints/linux.370

@@ -87,6 +87,11 @@ CFLAGS+=-fsanitize=address
 LFLAGS+=-fsanitize=address
 endif
 
+ifeq "$(USE_UBSAN)" "1"
+CFLAGS+=-fsanitize=undefined
+LFLAGS+=-fsanitize=undefined
+endif
+
 ifeq "$(USE_CURSESLIB)" "1"
 # default
 CURSESLIB = -lncurses -ltinfo