`gemmt` missing from docs about extensions

[david-cortes]

Non-standard BLAS extension GEMMT was added in the latest version of OpenBLAS:
#3796

But this function is not mentioned in the wiki for OpenBLAS extensions:
https://github.com/xianyi/OpenBLAS/wiki/OpenBLAS-Extensions

It's also currently missing from the cblas.h header shipped by libopenblas-openmp-dev in debian12, but readelf confirms that the .so file contains the cblas and fortran variants of this new addition.

[martin-frbg]

Yes, this has become intentional as the implementation in 0.3.23 turned out to be not fully functional. Header and wiki will be updated with 0.3.24