Respect app-alternatives/ninja (n2 is not yet in the tree) and
user variables from the ninja-utils eclass.
This is a workaround. A proper implementation similar to
the LTO implementation (c6f429) should allow the build system to be set at
configure time.

From: Lucio Sauer <watermanpaint@posteo.net>
--- a/build/ninja_gen/src/build.rs
+++ b/build/ninja_gen/src/build.rs
@@ -49,7 +49,7 @@ impl Build {
             output_text: Default::default(),
             action_names: Default::default(),
             groups: Default::default(),
-            have_n2: which::which("n2").is_ok(),
+            have_n2: false,
         };
 
         build.add_action("build:configure", ConfigureBuild {})?;
--- a/build/runner/src/build.rs
+++ b/build/runner/src/build.rs
@@ -56,6 +56,11 @@ pub fn run_build(args: BuildArgs) {
 
     let start_time = Instant::now();
     let mut command = Command::new(get_ninja_command());
+
+    if env::var("NINJA_VERBOSE").unwrap_or(String::from("ON")).eq("ON") {
+        command.arg("-v");
+    }
+
     command
         .arg("-f")
         .arg(&build_file)
@@ -112,11 +117,7 @@ pub fn run_build(args: BuildArgs) {
 }
 
 fn get_ninja_command() -> &'static str {
-    if which::which("n2").is_ok() {
-        "n2"
-    } else {
-        "ninja"
-    }
+    "ninja"
 }
 
 fn setup_build_root() -> Utf8PathBuf {