[Support] Accept macosx triple as 'darwin' in Host unittest. NFC.

If LLVM was configured with an x86_64-apple-macosx host triple, this
test would fail, as the API works but the triple isn't in the whitelist.

llvm-svn: 293990

llvm/unittests/Support/Host.cpp

@@ -35,6 +35,7 @@ class HostTest : public testing::Test {
     // x86_64 Linux and Darwin.
     SupportedArchAndOSs.push_back(std::make_pair(Triple::x86_64, Triple::Linux));
     SupportedArchAndOSs.push_back(std::make_pair(Triple::x86_64, Triple::Darwin));
+    SupportedArchAndOSs.push_back(std::make_pair(Triple::x86_64, Triple::MacOSX));
   }
 };