[9] Backport approval request: 8078470: [Linux] Replace syscall use in os::fork_and_exec with glibc fork() and execve()

[David Holmes]

This is the "backport" to 9 as the original change had to go into 8u 
first for logistical/scheduling reasons.

Bug: https://bugs.openjdk.java.net/browse/JDK-8078470

8u changeset: 
http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/rev/915ca3e9d15e

Original review thread: 
http://mail.openjdk.java.net/pipermail/hotspot-dev/2015-April/018171.html


The changeset mostly applied cleanly with some manual tweaking in one 
spot as the 9 code refers to AARCH64 where the 8u code does not.

Thanks,
David