d: Fix undefined template references with circular module imports

d: Fix undefined template references with circular module imports

In `TemplateInstance::semantic`, there exists special handling of
matching template instances for the same template declaration to ensure
that only at most one instance gets codegen'd.

If the primary instance `inst` originated from a non-root module, the
`minst` field will be updated so it is now coming from a root module,
however all Dsymbol `inst->members` of the instance still have their
`_scope->minst` pointing at the original non-root module. We must now
propagate `minst` to all members so that forward referenced dependencies
that get instantiated will also be appended to the root module,
otherwise there will be undefined references at link-time.

This doesn't affect compilations where all modules are compiled
together, as every module is a root module in that situation.  What this
primarily affects are cases where there is a mix of root and non-root
modules, and a template was first instantiated in a non-root context,
then later instantiated again in a root context.

gcc/d/ChangeLog:

	* dmd/dtemplate.c (TemplateInstance::semantic): Propagate the root
	module where the instantiated template should belong from the instance
	to all member scopes.

gcc/testsuite/ChangeLog:

	* gdc.test/compilable/imports/test21299/func.d: New test.
	* gdc.test/compilable/imports/test21299/mtype.d: New test.
	* gdc.test/compilable/imports/test21299/rootstringtable.d: New test.
	* gdc.test/compilable/test21299a.d: New test.
	* gdc.test/compilable/test21299b.d: New test.
	* gdc.test/compilable/test21299c.d: New test.
	* gdc.test/compilable/test21299d.d: New test.

(cherry picked from commit e419ede8915eeb879de3d9c026cd4213aaceb86a)