[foreign-jextract] Integrated: 8252899: jextract can't handle multiple extern declarations that have the same name, but a different type name

[Jorn Vernee]

Hi,

This PR let's jextract handle cases like the one described in the bug:

    typedef int MyInt;

    extern const int x;
    extern const MyInt x;

Where the same global variable is re-declared, but slightly differently.

The current code is de-duping globals using the declaration. Changing this to de-duping by name allows use to also
handle these cases.

Thanks,
Jorn

-------------

Commit messages:
 - Dedupe global variables just by name instead of by decl, allowing redefinition of globals with the same type but under a different name (typedef).

Changes: https://git.openjdk.java.net/panama-foreign/pull/313/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=313&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252899
  Stats: 64 lines in 3 files changed: 58 ins; 2 del; 4 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/313.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/313/head:pull/313

PR: https://git.openjdk.java.net/panama-foreign/pull/313