[foreign] RFR 8211924: Tweak Panama/foreign build to be friendly with automated build and test

[Maurizio Cimadamore]

Hi,
this patch (contributed by Erik Joelsson) tweaks the Panama/foreign 
build to be friendly with our automated build and test infra. As it can 
be seen a step has been added to build the relevant clang libraries on 
systems such as Linux - which were failing to build when using the 
supplied devkit.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8211924/

Cheers
Maurizio