RFR: JDK-8200357 Inline SoundLibraries.gmk into Lib-java.desktop.gmk

[Magnus Ihse Bursie]

With some further simplifications, the code for building libjsound is 
very small. There is no longer any reason to have that in a separate 
file. Instead it should be inlined into Lib-java.desktop.gmk.

This patch also includes code to stop building libjsig on AIX, as 
requested by Thomas Stüfe.

Bug: https://bugs.openjdk.java.net/browse/JDK-8200357
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8200357-inline-SoundLibraries/webrev.01

/Magnus