Make genearation of libconstants.c more robust

Changes to the clang build flags passed into
can cause compile errors for the generated libconstants.c. Make
this process more robust by:

1. Typecasting values to unsigned long to address compiler failures
   when other integer types are added to libconstants.c.
2. Making the grep statement filter out constants defined
   without a value but with trailing whitespace e.g.
   "#define ANDROID_API_H ".

Change-Id: I91d65db70b9e267882a8f381a836bbd7caded22e
1 file changed