Construct MulAddMul at gemm_wrapper! call sites (#34601)
* Construct MulAddMul at gemm_wrapper! call sites
* Add branches manually in MulAddMul constructor
This is suggested by chethega in:
https://github.com/JuliaLang/julia/pull/29634#discussion_r314010599
* Update stdlib/LinearAlgebra/src/generic.jl
Co-Authored-By: Kristoffer Carlsson <kristoffer.carlsson@chalmers.se>
Co-authored-by: Kristoffer Carlsson <kristoffer.carlsson@chalmers.se>
