Allow stripping of dead code

The `-Clink-dead-code` flag was added to fix an error with certain
targets.

However, it can also cause problems.

Example: You depend on crate A which links to library B. A includes an
unused reference to `B::foo`. If the specific version of B we have is
missing `foo`, we now get a linker error whereas we would not if
stripping dead code.

Author: Paho Lurie-Gregg

Diff for: src/options.rs

@@ -123,6 +123,11 @@ pub struct BuildOptions {
     /// The attribute takes a default value `false`, ensuring that by default,
     /// the coverage option will be disabled).
     pub coverage: bool,
+
+    /// Dead code is linked by default to prevent a potential error with some
+    /// optimized targets. This flag allows you to opt out of it.
+    #[structopt(long)]
+    pub strip_dead_code: bool,
 }
 
 impl stdfmt::Display for BuildOptions {
@@ -200,6 +205,7 @@ mod test {
             unstable_flags: Vec::new(),
             target_dir: None,
             coverage: false,
+            strip_dead_code: false,
         };
 
         let opts = vec![

Diff for: src/project.rs

@@ -162,10 +162,13 @@ impl FuzzProject {
                                      -Cllvm-args=-sanitizer-coverage-level=4 \
                                      -Cllvm-args=-sanitizer-coverage-trace-compares \
                                      -Cllvm-args=-sanitizer-coverage-inline-8bit-counters \
-                                     -Cllvm-args=-sanitizer-coverage-pc-table \
-                                     -Clink-dead-code"
+                                     -Cllvm-args=-sanitizer-coverage-pc-table"
             .to_owned();
 
+        if !build.strip_dead_code {
+            rustflags.push_str(" -Clink-dead-code");
+        }
+
         if build.coverage {
             rustflags.push_str(" -Zinstrument-coverage");
         }

Diff for: tests/tests/main.rs

@@ -810,3 +810,29 @@ fn build_dev() {
     assert!(a_bin.is_file());
     assert!(b_bin.is_file());
 }
+
+#[test]
+fn build_stripping_dead_code() {
+    let project = project("build_strip").with_fuzz().build();
+
+    // Create some targets.
+    project
+        .cargo_fuzz()
+        .arg("add")
+        .arg("build_strip_a")
+        .assert()
+        .success();
+
+    project
+        .cargo_fuzz()
+        .arg("build")
+        .arg("--strip-dead-code")
+        .arg("--dev")
+        .assert()
+        .success();
+
+    let build_dir = project.fuzz_build_dir().join("debug");
+
+    let a_bin = build_dir.join("build_strip_a");
+    assert!(a_bin.is_file(), "Not a file: {}", a_bin.display());
+}