Build 2020.2-15171-g4655dd6ce3

[intel-npu] Fix build when using specific Werror (#24250)

The commit eb025fad1e800280746eb2d543818bece701c9c6 breaks the build
when `CXXFLAGS` or `CFLAGS` have a specific `-Werror` flag.

For example, when `CXXFLAGS` have `-Werror=format-security`, the build
fails with this message:

```
c++: warning: =format-security: linker input file unused because linking not done
c++: error: =format-security: linker input file not found: No such file or directory
```

That's because every occurrence of the `-Werror` string is being
replaced in the original `CXXFLAGS` and `CFLAGS` variables. So, if they
contain `-Werror=<something>`, it will become just `=<something>`, which
will be an unrecognized option.

The current commit fixes this by appending `-Wno-error` to `CXXFLAGS`
and `CFLAGS` to properly disable errors on warnings.