Add support of ARC architecture

[abrodkin]

More info about ARC architecture is here: [1] & [2].
We need ARC supported here for many things like:

• ICU (see [3])
• Qt5 etc

[1] https://www.synopsys.com/designware-ip/processor-solutions/arc-processors.html
[2] https://en.wikipedia.org/wiki/ARC_(processor)
[3] https://unicode-org.atlassian.net/browse/ICU-20155

Fixes #81

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[floitsch]

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