Config option for allowing undefined behavior

config/config-options/DUK_USE_ALLOW_UNDEFINED_BEHAVIOR.yaml

@@ -0,0 +1,10 @@
+define: DUK_USE_ALLOW_UNDEFINED_BEHAVIOR
+introduced: 2.3.0
+default: false
+tags:
+  - portability
+description: >
+  Allow technically undefined behavior such as out-of-range double-to-integer
+  casts, floating point division by zero, etc. which are likely to work on the
+  majority of platforms.  Default is to avoid such behaviors, at the cost of
+  some footprint and performance.

config/examples/low_memory.yaml

@@ -15,6 +15,12 @@
 # memory layout if the architecture supports it.
 #DUK_USE_ALIGN_BY: 1
 
+# With the vast majority of compilers some of the 'undefined behavior'
+# assumptions are fine, and produce smaller and faster code, so enable
+# by default for lowmem targets.  You may need to disable this for some
+# compilers.
+DUK_USE_ALLOW_UNDEFINED_BEHAVIOR: true
+
 DUK_USE_PREFER_SIZE: true
 DUK_USE_EXEC_PREFER_SIZE: true
 DUK_USE_FAST_REFCOUNT_DEFAULT: false