build: remove spam generated by link task

Simply override the cprogram Task's __str__ method with our own implementation.
This is way easier on the eyes when compiling mpv during development, since
warnings are not pushed outside of your average screenful of content.

waftools/waf_customizations.py

@@ -34,6 +34,10 @@ def build(ctx):
     class cprogram(cls):
         run_str = cls.hcode + '${LAST_LINKFLAGS}'
 
+        def __str__(self):
+            tgt_str = ' '.join([a.nice_path() for a in self.outputs])
+            return 'linking -> {0}\n'.format(tgt_str)
+
     cls = Task.classes['macplist']
     class macplist(cls):
         def run(self):