Add -Wextra warning flag.

Fix triggered warnings:
- unused parameter
- type qualifiers ignored on function return type
- missing initializer for member

1 files changed, 1 insertions, 1 deletions

diff --git a/src/subprocess.cc b/src/subprocess.cc
index 74eded0..da93b1f 100644
--- a/src/subprocess.cc
+++ b/src/subprocess.cc
@@ -37,7 +37,7 @@ Subprocess::~Subprocess() {
     Finish();
 }
 
-bool Subprocess::Start(SubprocessSet* set, const string& command) {
+bool Subprocess::Start(SubprocessSet* /* set */, const string& command) {
   int output_pipe[2];
   if (pipe(output_pipe) < 0)
     Fatal("pipe: %s", strerror(errno));