[8u] RFR: modified backport of 8138820: JDK Hotspot build fails with Xcode 7.0.1

[Simon Tooke]

Hello all,

This is an odd request, there are 3 different issues surrounding the optimized compilation of two files when using clang.
These three issues attempt to ensure loopTransform.cpp and unsafe.cpp are not compiled optimized due to a bug in clang.

(Before this, the test was for clang version 4)

Add test for 4.2, 5.0 and 5.1
https://bugs.openjdk.java.net/browse/JDK-8048298 <https://bugs.openjdk.java.net/browse/JDK-8048298> 8048298: Clang needs to lower optimization level for some files

Add test for 6.0
https://bugs.openjdk.java.net/browse/JDK-8055838 <https://bugs.openjdk.java.net/browse/JDK-8055838> 8055838: Hotspot does not compile with clang 6.0 (OS X Yosemite)

Any clang <= 7.1
https://bugs.openjdk.java.net/browse/JDK-8138820 <https://bugs.openjdk.java.net/browse/JDK-8138820> 8138820: JDK Hotspot build fails with Xcode 7.0.1

Throw hands in the air and just avoid optimizing these two files when using clang:
https://bugs.openjdk.java.net/browse/JDK-8152666 <https://bugs.openjdk.java.net/browse/JDK-8152666> 8152666: The new Hotspot Build System

Now, I do not wish to port the 8152666 (The new Hotspot Build System) (71 files!) down to 8u, but I do with to remove checks for clang versions.
In the current JDK head, there are no checks.  Until clang is fixed and verified, this is as it should be in 8u. I believe.

I am framing this as a backport of 8138820, but I admit it’s a bit different.
Proposed web rev: http://cr.openjdk.java.net/~stooke/webrevs/jdk-8138820-jdk8u/00/hotspot.00/ <http://cr.openjdk.java.net/~stooke/webrevs/jdk-8138820-jdk8u/00/hotspot.00/>

I have not tested clang to see if the issue is still there, or indeed if it is an issue with clang.  But, the build system does believe there
Is an ongoing issue fixed by this patch (and I have heard this in casual conversation), and so I propose it for 8u.
I believe it’s best to be conservative here.

Thank you for reading this far - please let me know what you think.

-Simon