tsan: fix free_race3.c test

PPC64 bot failed with the following error.
The buildbot output is not particularly useful,
but looking at other similar tests, it seems
that there is something broken in free stacks on PPC64.
Use the same hack as other tests use to expect
an additional stray frame.

/home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/test/tsan/free_race3.c:28:11: error: CHECK: expected string not found in input
// CHECK: Previous write of size 4 at {{.*}} by thread T1{{.*}}:
          ^
<stdin>:13:9: note: scanning from here
 #1 main /home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/test/tsan/free_race3.c:17:3 (free_race3.c.tmp+0x1012fab8)
        ^
<stdin>:17:2: note: possible intended match here
ThreadSanitizer: reported 1 warnings
 ^

Input file: <stdin>
Check file: /home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/test/tsan/free_race3.c

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            .
            .
            .
            8:  Previous write of size 4 at 0x7ffff4d01ab0 by thread T1:
            9:  #0 Thread /home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/test/tsan/free_race3.c:8:10 (free_race3.c.tmp+0x1012f9dc)
           10:
           11:  Thread T1 (tid=3222898, finished) created by main thread at:
           12:  #0 pthread_create /home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/lib/tsan/rtl/tsan_interceptors_posix.cpp:1001:3 (free_race3.c.tmp+0x100b9040)
           13:  #1 main /home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/test/tsan/free_race3.c:17:3 (free_race3.c.tmp+0x1012fab8)
check:28'0             X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
           14:
check:28'0     ~
           15: SUMMARY: ThreadSanitizer: data race /home/buildbots/ppc64le-clang-lnt-test/clang-ppc64le-lnt/llvm/compiler-rt/test/tsan/free_race3.c:19:3 in main
check:28'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           16: ==================
check:28'0     ~~~~~~~~~~~~~~~~~~~
           17: ThreadSanitizer: reported 1 warnings
check:28'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:28'1      ?                                    possible intended match
>>>>>>

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D112444