Log Message:
devel/opal: Remove CFLAG -D__STDC_CONSTANT_MACROS

This CFLAG, added 2011/02/06, was treating a symptom of the UINT64_C
problem with ffmpeg, which was fixed on 2011/11/22 (2011/11/26).
Since then, opal has been emitting a warning that __STDC_CONSTANT_MACROS
is redefined and removing the redundant CFLAG silences the warning.