Add bool to PrimType

[phadej]

C99 extended this set by adding the Boolean type _Bool

(and stdbool.h contains #define bool _Bool)

more recent libclang also treat bool as a keyword.

EDIT: we see something like

    = MkCATypedefStruct {cATypedefStruct_field_0 :: CBool',

in distilled_lib_1 test case. That field is bool.

This is related to #134, while uint64_t is usually a typedef, bool is a macro define at least in musl and glibc on my machine (maybe it's even standard saying it has to be CPP macro?)