[SV 65777] Add more const

[SV 65777] Add more const

Add more const to static arrays.  On some systems this allows more
data to be placed in RO segments and shared between multiple
instances of the make executable.  Anyway more const is good hygiene.

* src/default.c: Add const to arrays.
* src/function.c: Ditto.
* src/hash.c: Ditto.
* src/hash.h: Ditto.
* src/job.c: Ditto.
* src/read.c: Ditto.
* src/remake.c: Ditto.
* src/rule.c: Ditto.
* src/rule.h: Ditto.