[SanitizeCoverage] Enable stack-depth coverage for -fsanitize=fuzzer

Summary:
- Don't sanitize __sancov_lowest_stack.
- Don't instrument leaf functions.
- Add CoverageStackDepth to Fuzzer and FuzzerNoLink.
- Disable stack depth tracking on Mac.

Reviewers: vitalybuka, kcc, george.karpenkov

Reviewed By: kcc

Subscribers: kubamracek, cfe-commits, llvm-commits, hiraditya

Differential Revision: https://reviews.llvm.org/D37156

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@312026 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Driver/SanitizerArgs.cpp

@@ -291,9 +291,13 @@ SanitizerArgs::SanitizerArgs(const ToolChain &TC,
         Add |= FuzzerNoLink;
 
       // Enable coverage if the fuzzing flag is set.
-      if (Add & FuzzerNoLink)
+      if (Add & FuzzerNoLink) {
         CoverageFeatures |= CoverageTracePCGuard | CoverageIndirCall |
                             CoverageTraceCmp | CoveragePCTable;
+        // Due to TLS differences, stack depth tracking is disabled on Mac.
+        if (!TC.getTriple().isOSDarwin())
+          CoverageFeatures |= CoverageStackDepth;
+      }
 
       Kinds |= Add;
     } else if (Arg->getOption().matches(options::OPT_fno_sanitize_EQ)) {