Chained import with import ... from ... generates invalid C++ names

[bbannier]

The following reproducer with chained imports produces names which cannot be found. Looking at the generated name it looks like this is due to us generating namespace names for hooks by concatenating the module names in the import chain, but use types in simple namespaces.

# @TEST-EXEC: spicyc -d -j z.spicy -o z.hlto

module z;
import y;

@TEST-START-FILE y.spicy
module y;
import x from bla;
@TEST-END-FILE

@TEST-START-FILE bla/x.spicy
module x;

type X = unit {
	on %done {}
};
@TEST-END-FILE

Bisecting with this reproducer points to #1195 as the change introducing this regression.