RFR: 8042088: Sjavac spawns external processes in a unnecessarily complex and platform dependent way

[Andreas Lundblad]

Hi compiler-dev,

Please review this small fix for JDK-8042088 which changes how sjavac spawns background processes.

Description:
Sjavac starts a background server through a shell (cmd on windows, and /bin/sh on other systems). This patch changes this so that the background service is launched directly instead.

Link to webrev:
http://cr.openjdk.java.net/~alundblad/8042088

Link to bug report:
https://bugs.openjdk.java.net/browse/JDK-8042088

-- Andreas