RFR (tedious) 8216022: Use #pragma once

[Leo Korinth]

I like this change.

It is _safer_. It creates cleaner, shorter headers. It eases creation, 
renaming and moving of header files. It makes refactoring easier and 
more importantly eases review. There is only one style of it so no need 
to force people to use the "correct" style.

Let us make use of #pragma once and thus helping it on its way to become 
part of the standard!

Thanks,
Leo

On 03/01/2019 03:31, coleen.phillimore at oracle.com wrote:
> 
> Here is the webrev and bug link.
> 
> open webrev at http://cr.openjdk.java.net/~coleenp/8216022.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8216022
> 
> On 1/2/19 9:16 PM, coleen.phillimore at oracle.com wrote:
>> Summary: change include guards to #pragma once, except in generated 
>> header files.
>>
>> Tested with mach5 for linux-x64{-debug}, solaris-sparc, macosx-x64, 
>> windows-x64, built aarch64 with cross compiler, and zero.
>>
>> Ran tier1 and 2 tests.
>>
>> The webrev is huge but there are only 3 lines changed in each header 
>> file.  So click on the patch.
>>
>> I'll update the copyright headers with a script with the commit. Also, 
>> will do this after the shenandoah copyright headers are fixed.
>>
>> Adrian: I included you to check your platforms.
>>
>> Happy New Year!
>> Coleen
>