[sanitizer-coverage] Stop marking this test as unsupported on Darwin
The bug that was causing this to fail was fixed in r305429.
// Tests -fsanitize-coverage=inline-8bit-counters
//
// REQUIRES: has_sancovcc,stable-runtime
-// UNSUPPORTED: i386-darwin, x86_64-darwin, x86_64h-darwin
+// UNSUPPORTED: i386-darwin
//
// RUN: %clangxx -O0 %s -fsanitize-coverage=inline-8bit-counters 2>&1
