ast: Turn VAR + STATIC/EXTERN attribs into VAR, EXTERNVAR, STATICVAR
c: Accept initializers on vars too, not only params
c: Support bitfields
Add support for nested named structs
c: Parse struct bodies as part of cBaseType()
ast: Fix broken declaration of astIsEqual() flags
Use better dummy id for unnamed structs

No need to include fbfrog in the name. It should have the double _
underscore prefix because that's reserved in C, so most likely won't be
used, but that's all it needs.
Add test case for merging of nested named structs
Slightly improve merging of unnamed structs by using typedefs
ast: Fix broken subtype check for symbol renaming
ast: Add helper for replacing subtypes
ast: Fix wrong recursion in hReplaceTypes()
ast: Remove redundant subtype updating code
ast: Improve merging of unnamed structs by updating references