RFR: 8192123: Zero should use compiler built-ins for atomics on linux-arm

[John Paul Adrian Glaubitz]

Hi!

Like it has already been done for linux-m68k in JDK-8187227, Zero should also be
patched on linux-arm to use compiler built-ins for the atomic functions in
hotspot/os_cpu/linux_zero/assembler_linux_zero.cpp.

Since the compiler built-ins for cmpxchg() work exactly like the current ARM-specific
implementation in Zero, there is no need anymore to carry our own implementation but
rather rely on gcc which helps simplifying the code.

I have successfully tested this change in the following targets:

- Linux ARMv4T
- Linux ARMv7

My change also removes a single empty line to make the formatting more
consistent. Hope this is ok.

The webrev can be found in [1].

Thanks,
Adrian

> [1] http://cr.openjdk.java.net/~glaubitz/8192123/webrev.00/

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  .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz at debian.org
`. `'   Freie Universitaet Berlin - glaubitz at physik.fu-berlin.de
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