Link to dcc-rs dependencies

When linking against the static library we need to also include all
dynamic libs this still depends on.  Thanks to the old CI system
spotting this!

python/src/deltachat/_build.py

@@ -10,7 +10,7 @@ def ffibuilder():
     projdir = os.environ.get('DCC_RS_DEV')
     target = os.environ.get('DCC_RS_TARGET', 'release')
     if projdir:
-        libs = []
+        libs = ['rt', 'dl', 'm']
         objs = [os.path.join(projdir, 'target', target, 'libdeltachat.a')]
         incs = [os.path.join(projdir, 'deltachat-ffi')]
     else: