use_default_rpm_opt_flags. It defaults to a value of 1, meaning that
we'll try to use $RPM_OPT_FLAGS. But if you're not compiling with the
GNU compilers, you might want to set this value to 0 so that your
compiler doesn't get flags that it doesn't understand (e.g., PGI 7.0
will barf on flags that it doesn't understand).
This commit was SVN r14477.