[compiler-rt] Disable failing test on darwin during investigation.

[compiler-rt] Disable failing test on darwin during investigation.

/Users/buildslave/jenkins/workspace/clang-stage1-configure-RA/llvm/projects/compiler-rt/test/asan/TestCases/Posix/bcmp_test.cc:14:12: error: CHECK: expected string not found in input
 // CHECK: {{#1.*bcmp}}
           ^
<stdin>:2:57: note: scanning from here
==34677==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffee93777c4 at pc 0x0001068a7285 bp 0x7ffee9377770 sp 0x7ffee9376ef8
                                                        ^
<stdin>:6:20: note: possible intended match here
 #2 0x106888e77 in main bcmp_test.cc:12
                   ^

llvm-svn: 354888