Fix compile errors and warnings when "thread" is disabled. (#134)

Fix errors and warnings in c-scape/src/stdio.rs when the "thread"
feature is disabled.

c-scape/src/stdio.rs

@@ -576,6 +576,11 @@ unsafe extern "C" fn flockfile(file: *mut libc::FILE) {
     {
         (*file.cast::<FILE>()).flockfile_mutex.lock();
     }
+
+    #[cfg(not(feature = "thread"))]
+    {
+        let _ = file;
+    }
 }
 
 #[no_mangle]
@@ -586,6 +591,11 @@ unsafe extern "C" fn funlockfile(file: *mut libc::FILE) {
     {
         (*file.cast::<FILE>()).flockfile_mutex.unlock();
     }
+
+    #[cfg(not(feature = "thread"))]
+    {
+        let _ = file;
+    }
 }
 
 #[no_mangle]
@@ -600,6 +610,12 @@ unsafe extern "C" fn ftrylockfile(file: *mut libc::FILE) -> c_int {
             -1
         }
     }
+
+    #[cfg(not(feature = "thread"))]
+    {
+        let _ = file;
+        0
+    }
 }
 
 #[no_mangle]