Estimated hours taken: 4
Branches: main, version-0_10_y

Fix a bug where the C code that we generated contained a type error
which showed up when using non-GCC C compilers.

runtime/mercury_string.h:
runtime/mercury_misc.c:
	Change the argument type for MR_hash_string() from MR_Word to
	MR_ConstString, to match the code that the MLDS back-end generates
	(and common sense).

runtime/mercury_tabling.c:
compiler/llds.m:
	Update to match the change to runtime/mercury_string.h.