Remove core.a before rebuilding it

Before, the ar command was just ran for all .o files that should end up
in core.a, which should replace any old code in core.a. However, it
seems that in the unlikely event that functions or entire source files
are deleted, they might linger in the core.a file.

Author: matthijskooijman

app/src/processing/app/debug/Compiler.java

@@ -703,13 +703,19 @@ void compileCore()
     if (variantFolder != null)
       includeFolders.add(variantFolder);
 
+    File afile = new File(buildFolder, "core.a");
+
     List<File> coreObjectFiles = compileFiles(buildFolder, coreFolder, true,
                                               includeFolders);
+
+    // Delete the .a file, to prevent any previous code from lingering
+    afile.delete();
+
     for (File file : coreObjectFiles) {
 
       PreferencesMap dict = new PreferencesMap(prefs);
       dict.put("ide_version", "" + Base.REVISION);
-      dict.put("archive_file", "core.a");
+      dict.put("archive_file", afile.getName());
       dict.put("object_file", file.getAbsolutePath());
 
       String[] cmdArray;