[foreign-jextract] RFR: 8277645: TreeMaker should not call type() on pointer types too early

[Maurizio Cimadamore]

This patch fixes a couple of callsites in TreeMaker which were calling `DelegatedType::type`.

`DelegatedType` is a common supertype for both typedef types and pointer types. The reason why `TreeMaker` calls that method is to recover the *canonical* type of a typedef.

Unfortunately, as `TreeMaker` doesn't check the delegated type kind, it can sometime call `type()` on a delegated type whose kind is `POINTER`. The way in which the jextract parser is setup is such that pointee types can only be accessed *after* parsing has completed.

This issue only occurs under very rare circumstances, that is when a type qualifier (other than the usual ones, such as `const`) is used on a pointer typedef - such as `__ptr64`. In such cases, the clang AST sees an `AttributedType` and not a `QualifiedType`, which throws our parsing logic off-guard.

The solution is to check for the delegated type kind before attempting to call `type()`, and only call it when its kind is `TYPEDEF`. To test this I used the special clang flag `-fms-extensions` which allows to use the MS extensions even on Linux/Mac.

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Commit messages:
 - Fix TreeMaker not to call type() on potentially unresolved pointers

Changes: https://git.openjdk.java.net/panama-foreign/pull/616/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=616&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277645
  Stats: 60 lines in 3 files changed: 50 ins; 5 del; 5 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/616.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/616/head:pull/616

PR: https://git.openjdk.java.net/panama-foreign/pull/616