Create "DEFAULT" build subdir if neither build dir nor build profile are specified.

Author: bmcdonnell-ionx

mbed/mbed.py

@@ -2498,14 +2498,15 @@ def compile_(toolchain=None, target=None, profile=False, compile_library=False,
         build_path = build
 
         def safe_append_profile_to_build_path(bp):
+            append_str = 'DEFAULT'
+
             if profile:
                 if isinstance(profile, basestring):
                     append_str = profile
                 else:
                     append_str = profile[0]
 
-                if append_str:
-                    bp = os.path.join(bp, os.path.splitext(os.path.basename(append_str))[0].upper())
+            bp = os.path.join(bp, os.path.splitext(os.path.basename(append_str))[0].upper())
 
             return bp