Hello -

We're facing an issue where non-RPM builds using sip fail because RPM-specific compiler and linker flags are embedded in sipconfig.py. This is probably not a problem for downstream RPM builds which use sip because the necessary environment variables are defined.

Specifically, we see the following compilation failure message:
```
g++: fatal error: environment variable ‘RPM_ARCH’ not defined
```

This seems to be caused by the inclusion of one or more RPM-specific `-specs=...` flags in the captured compile flags in sipconfig.py. I don't have a full understanding of why these flags need to be captured and used when compiling downstream code using sip, but I don't think these flags should be present.

We were able to work around the problem by specifically removing the `-specs=...` flags from the captured flags during sip's build. I've attached a patch which does this, which I hope can be used to arrive at an acceptable solution.

Reproducible: Always