RFR(XS): 8214120: [REDO] Fix sun.awt.nativedebug on X11 platforms

[Volker Simonis]

Hi,

so here's a reworked version of my previous change:

http://cr.openjdk.java.net/~simonis/webrevs/2018/8214120/
https://bugs.openjdk.java.net/browse/JDK-8214120

In addition to my initial change (which unfortunately broke the
Solaris build) the new version has to JNIEXPORT the following methods
from libawt.so otherwise they won't be visible in libawt_xawt.so on
some platforms which make symbols local by default (e.g. Solaris):

DAssert_Impl
DTrace_PrintFunction
DTrace_VPrint
DTrace_VPrintln

Local tests on Linux/AIX and Solaris succeeded. The patch is currently
building in the submit repo.

Thank you and best regards,
Volker