[build.py] debug-info prevents compilation for GCC_ARM

[geky]

Ran the following:

$ PYTHONPATH=. python tools/build.py -t GCC_ARM -m K64F
[WARNING] Using default settings. Define your settings in the file "./mbed_settings.py"
Building library CMSIS (K64F, GCC_ARM)
Copy: core_cm4_simd.h
Copy: arm_math.h
Copy: core_cm0plus.h
blablablabla

Works just fine.

But oh no! Someone (not me I assure you) put a bug in my program. Time to debug.

Ran the following to add debug info:

$ PYTHONPATH=. python tools/build.py -t GCC_ARM -m K64F -o debug-info
[WARNING] Using default settings. Define your settings in the file "./mbed_settings.py"
GCC_ARM instance has no attribute 'notify_fun'

Completed in: (0.00)s

Build failures:
  * GCC_ARM::K64F

Here's some random info:

• git log -n1 --oneline: f864b84 Merge pull request Fix K64F-based config tests #1983 from mbedmicro/fix_config_tests
• python --version: Python 2.7.11+
• cat /proc/version: Ubuntu 5.3.1-14ubuntu2.1

[theotherjimmy]

That cat /proc/version is just the gcc version. it should look something like this:
Linux version 3.13.0-66-generic (buildd@lgw01-26) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #108-Ubuntu SMP Wed Oct 7 15:20:27 UTC 2015

[screamerbg]

LGTM