[zorg][PowerPC] Switch RHEL buildbot to use runtime build

We are using runtime build now,
See Petr's definition about "runtime" build here:
http://lists.llvm.org/pipermail/llvm-dev/2020-April/140771.html

Update the cmake macros to reflect the change.

Reviewed By: saghir

Differential Revision: https://reviews.llvm.org/D90609
1 file changed