[foreign] RFR 8216483: jextract tests have to be modified to run on Windows platform

[Jorn Vernee]

Hi,

Continuation of [1].

updated webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/windows_tests/webrev.04/

For the TestJextractFFI test I'm now just checking the operating system 
in the LibClang.java patch file:

     String libName = System.getProperty("os.name").startsWith("Windows")
             ? "libclang"
             : "clang";
     Library libclang = Libraries.loadLibrary(MethodHandles.lookup(), 
libName);

The other problem is that the dll is in the bin folder vs lib folder on 
Windows, and the test was using the linker path which is the lib folder 
on Windows. There was no build system variable available for the folder 
that contains the library file, so instead I'm deriving it from the 
library file path.

Cheers,
Jorn

[1] : 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-January/003691.html