Move CMake build "target" closer to its use

There is another local variable called "target" -- the one for
compilation target platform. This variable is CMake build target.
Move it closer to the only place where it's used to avoid shadowing
the other "target", which will soon be needed.

Author: ilammy

src/lib.rs

@@ -787,7 +787,6 @@ impl Config {
         }
 
         // And build!
-        let target = self.cmake_target.clone().unwrap_or("install".to_string());
         let mut cmd = Command::new(&executable);
         cmd.current_dir(&build);
 
@@ -819,6 +818,7 @@ impl Config {
         cmd.arg("--build").arg(".");
 
         if !self.no_build_target {
+            let target = self.cmake_target.clone().unwrap_or("install".to_string());
             cmd.arg("--target").arg(target);
         }