A native build of a program that installs the C scanner but decodes no
reply, such as the self-hosted source parser and CommonJS checks, failed
at startup with "Cannot access 'valueEnd' before initialization": the
build left the module variable uninitialized because its only other use
was the assignment in useNativeJsonValueEnd, which checks it first.
The scanner is now a property of a constant object that the decoders
and useNativeJsonValueEnd read, so it is initialized in every program.
Chris Tate
3d4aeddb82