uvision - get_toolchain method regression fix

uvision uses default_toolchain, thus exporter needs to provide a method to
distinguish between ARM and uARM. Fixes #1686

Author: 0xc0170

workspace_tools/export/uvision4.py

@@ -44,6 +44,8 @@ class Uvision4(Exporter):
             # target is not supported yet
             continue
 
+    def get_toolchain(self):
+        return TARGET_MAP[self.target].default_toolchain
 
     def generate(self):
         """ Generates the project files """