The specific flag required by OpenCV but stripped by superenv is ```-Wno-narrowing```.
Some errors like:
```
/tmp/opencv-uUgm/opencv-2.4.7/modules/core/src/arithm.cpp:444:51: error: constant expression evaluates to 4294967295 which cannot be narrowed to type 'int'
      [-Wc++11-narrowing]
static int CV_DECL_ALIGNED(16) v64f_absmask[] = { 0xffffffff, 0x7fffffff, 0xffffffff, 0x7fffffff };
                                                  ^~~~~~~~~~
```
will arise without it.
Other formulae may require in addition some other ```-Wno-*``` flags.