Enable leak sanitizer builds for darwin

[fjricci]

Summary

Support for leak sanitizer on darwin has been added to
compiler-rt, this patch adds compiler support.

[compnerd]

Please add a test case. The change itself looks reasonable.

[fjricci]

Add test cases

lib/Driver/ToolChains/Darwin.cpp

void DarwinClang::AddLinkRuntimeLibArgs(const ArgList &Args,
   if (const Arg *A = Args.getLastArg(options::OPT_static_libgcc)) {
     getDriver().Diag(diag::err_drv_unsupported_opt) << A->getAsString(Args);
     return;
   }
 
   const SanitizerArgs &Sanitize = getSanitizerArgs();
   if (Sanitize.needsAsanRt())
     AddLinkSanitizerLibArgs(Args, CmdArgs, "asan");
+  if (Sanitize.needsLsanRt())
+    AddLinkSanitizerLibArgs(Args, CmdArgs, "lsan");
   if (Sanitize.needsUbsanRt())
     AddLinkSanitizerLibArgs(Args, CmdArgs, "ubsan");
   if (Sanitize.needsTsanRt())
     AddLinkSanitizerLibArgs(Args, CmdArgs, "tsan");
   if (Sanitize.needsStatsRt()) {
     StringRef OS = isTargetMacOS() ? "osx" : "iossim";
     AddLinkRuntimeLib(Args, CmdArgs,
                       (Twine("libclang_rt.stats_client_") + OS + ".a").str(),

 SanitizerMask Darwin::getSupportedSanitizers() const {
   const bool IsX86_64 = getTriple().getArch() == llvm::Triple::x86_64;
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;
   if (isTargetMacOS()) {
     if (!isMacosxVersionLT(10, 9))
       Res |= SanitizerKind::Vptr;
     Res |= SanitizerKind::SafeStack;
+    Res |= SanitizerKind::Leak;
     if (IsX86_64)
       Res |= SanitizerKind::Thread;
   } else if (isTargetIOSSimulator() || isTargetTvOSSimulator()) {
+    Res |= SanitizerKind::Leak;
     if (IsX86_64)
       Res |= SanitizerKind::Thread;
   }
   return Res;
 }
 
 void Darwin::printVerboseInfo(raw_ostream &OS) const {
   CudaInstallation.print(OS);
 }