[compiler-rt][builtins][PowerPC] Enable builtins tests on PowerPC 64 bit LE

This patch aims to enable the tests for the compiler-rt builtin functions (that
currently already exist within compiler-rt) for PowerPC 64bit LE (ppc64le).
Previously when unit tests are run, these tests would be reported as
UNSUPPORTED. This patch updates the REQUIRES line for each test (to enable for
ppc64le), and each test is linked against compiler-rt when running.

Differential Revision: https://reviews.llvm.org/D54449

llvm-svn: 349634