Mark sancov test as unsupported on Darwin

This test has been failing on all Darwin bots since it was introduced:
http://lab.llvm.org:8080/green/job/clang-stage1-configure-RA_check/32111

fatal error: error in backend: Global variable '__sancov_gen_' has an invalid section specifier '__DATA,__sancov_counters': mach-o section specifier requires a section whose length is between 1 and 16 characters.
Target: x86_64-apple-darwin15.6.0

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@304673 91177308-0d34-0410-b5e6-96231b3b80d8

Author: vedantk

test/sanitizer_common/TestCases/sanitizer_coverage_inline8bit_counter.cc

@@ -1,7 +1,7 @@
 // Tests -fsanitize-coverage=inline-8bit-counters
 //
 // REQUIRES: has_sancovcc,stable-runtime
-// UNSUPPORTED: i386-darwin
+// UNSUPPORTED: i386-darwin, x86_64-darwin
 //
 // RUN: %clangxx -O0 %s -fsanitize-coverage=inline-8bit-counters 2>&1