[TestMiBreak] Print a formatted string via printf in the test case.

Summary:
If the string is not formatted, these can happen when compiled with GCC:
1. If it is a null string "", then GCC completely removes the call to
printf even with -O0.
2. If the string is a single character string, say "\n" for example,
then GCC replaces the call to printf with a call to putchar.
3. If the string length is greater than 1, but is not formatted, then
GCC replaces the call to printf with a call to puts.

All the above will fail the test as we want a breakpoint on "printf" to
hit.

Test Plan: dotest.py -C gcc -p TestMiBreak

Reviewers: chying, ki.stfu

Reviewed By: ki.stfu

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9025

llvm-svn: 235034