[sanitizer-coverage] emit __sanitizer_cov_trace_pc_guard w/o a preceding 'if' by default. Update the docs, also add deprecation notes around other parts of sanitizer coverage

llvm-svn: 292862
diff --git a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
index 5b4b1fb..e34dd61 100644
--- a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -95,7 +95,7 @@
     "sanitizer-coverage-block-threshold",
     cl::desc("Use a callback with a guard check inside it if there are"
              " more than this number of blocks."),
-    cl::Hidden, cl::init(500));
+    cl::Hidden, cl::init(0));
 
 static cl::opt<bool>
     ClExperimentalTracing("sanitizer-coverage-experimental-tracing",