default "trace pc guard" coverage off

* Add -f(no-)sanitize-coverage-trace-pc-guard CLI flag which defaults to
  off. This value lowers to TracePCGuard = true (LLVM backend) and -Xclang
  -fsanitize-coverage-trace-pc-guard. These settings are not
  automatically included with -ffuzz.
* Add `Build.Step.Compile` flag for sanitize_coverage_trace_pc_guard
  with appropriate documentation.
* Add `zig cc` integration for the respective flags.
* Avoid crashing in ELF linker code when -ffuzz -femit-llvm-ir used
  together.

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/std/Build/Step/Compile.zig b/lib/std/Build/Step/Compile.zig
index 8e9f61cfff..4f504151c0 100644
--- a/lib/std/Build/Step/Compile.zig
+++ b/lib/std/Build/Step/Compile.zig
@@ -217,6 +217,14 @@ no_builtin: bool = false,
 /// Managed by the build runner, not user build script.
 zig_process: ?*Step.ZigProcess,
 
+/// Enables deprecated coverage instrumentation that is only useful if you
+/// are using third party fuzzers that depend on it. Otherwise, slows down
+/// the instrumented binary with unnecessary function calls.
+///
+/// To enable fuzz testing instrumentation on a compilation, see the `fuzz`
+/// flag in `Module`.
+sanitize_coverage_trace_pc_guard: ?bool = null,
+
 pub const ExpectedCompileErrors = union(enum) {
     contains: []const u8,
     exact: []const []const u8,
@@ -1656,6 +1664,7 @@ fn getZigArgs(compile: *Compile) ![][]const u8 {
 
     try addFlag(&zig_args, "PIE", compile.pie);
     try addFlag(&zig_args, "lto", compile.want_lto);
+    try addFlag(&zig_args, "sanitize-coverage-trace-pc-guard", compile.sanitize_coverage_trace_pc_guard);
 
     if (compile.subsystem) |subsystem| {
         try zig_args.append("--subsystem");