Add more lib dir search options for build script

Author: 9prady9

build.rs

@@ -357,10 +357,25 @@ fn blob_backends(conf: &Config, build_dir: &std::path::PathBuf) -> (Vec<String>,
     if conf.use_lib {
         let afpath  = match env::var("AF_PATH") {
             Ok(af_path) => PathBuf::from(&af_path),
-            Err(_)      => panic!("Error use_lib is defined, but AF_PATH is not defined"),
+            Err(_)      => {
+                println!("WARNING! USE_LIB IS DEFINED, BUT AF_PATH IS NOT FOUND,");
+                println!("         TRYING TO FIND LIBRARIES FROM KNOWN DEFAULT LOCATIONS");
+
+                if cfg!(target_os = "windows")
+                    PathBuf::from("C:/Program Files/ArrayFire/v3/")
+                } else {
+                    PathBuf::from("/usr/local/")
+                }
+            },
         };
+
         let libpath = afpath.join("lib");
         backend_dirs.push(libpath.to_str().to_owned().unwrap().to_string());
+
+        if !cfg!(target_os = "windows") {
+            backend_dirs.push(String::from("/opt/arrayfire-3/lib"));
+            backend_dirs.push(String::from("/usr/lib"));
+        }
     } else {
         backend_dirs.push(build_dir.join("package/lib").to_str().to_owned().unwrap().to_string());
     }
@@ -390,6 +405,7 @@ fn blob_backends(conf: &Config, build_dir: &std::path::PathBuf) -> (Vec<String>,
 
         //blob in opencl deps
         lib_file_to_check = if cfg!(windows) {WIN_OCL_LIB_NAME} else {UNIX_OCL_LIB_NAME};
+
         if backend_exists(&lib_dir.join(lib_file_to_check).to_string_lossy()) {
             if ! cfg!(target_os = "macos"){
                 backends.push("OpenCL".to_string());