[PPC64] r2 register shouldn't be clobbered in asm

[lbianc]

HHVM Version

3.24.7

Operating System and Version

Ubuntu 18.10 using gcc7 (https://gcc.gnu.org/gcc-7/changes.html)

Standalone code, or other way to reproduce the problem

Building

Expected result

Build success

Actual result

hphp/util/portability.h:203:25: error: PIC register clobbered by ‘r2’ in ‘asm’

[fredemmott]

@racardoso , @gut, @lbianc: are any of you supporting HHVM on PPC64?

[lbianc]

Yes, I'm going to send the patch to fix that.

[racardoso]

I guess the problem is here https://github.com/facebook/hhvm/blob/master/hphp/util/portability.h#L210 right? It should test the GCC version and do not clobber r2 on versions that doesn't allow clobber r2 (TOC pointer). We already have the same issue on GCC 5.4.1 with r30.