Refactor test and set of cps function qualifier

This is a first step to allow storing cps information in type attributes
instead of as a function qualifier.
Add __cps__ function type attribute
Support cps attribute anywhere in return type

Broken:
- check that inner functions are cps
- cps function pointers
Allow non-cps inner functions
Set cps attribute after function type when functionalizing goto

Since the attribute is part of the time, setting before is a no-op
(it is overwritten).
Remove cps type specifier

Use only type attribute __attribute__((cps)).
Refactor to prepare for cps function pointers
Add test for cps function pointers
Support cps function pointers
Fix cps attribute handling in --ecpc
Fix typedef cpc_function
Clean cps type attributes and function pointer types
More complex test for cps function pointers
Merge branch 'cps-type-attribute' into develop