[LLDB][PPC64] Fix single step and LldbGdbServer tests

[LLDB][PPC64] Fix single step and LldbGdbServer tests

Summary:
On PPC64, the tested functions were being entered through their local entry point, while the tests expected the program to stop at the function start address, that, for PPC64, corresponds to the global entry point.

To fix the issue, the test program was modified to call the functions to be tested through function pointers, which, on PPC64, force the calls through the global entry point, while not affecting the test on other platforms.

Reviewers: clayborg, labath

Reviewed By: labath

Subscribers: alexandreyy, lbianc

Differential Revision: https://reviews.llvm.org/D43768
Patch by Leandro Lupori <leandro.lupori@gmail.com>.

llvm-svn: 327013