peakflops: make eltype a static parameter of the method

Otherwise `eltype` is inferred as merely `DataType`. Too bad that
constprop doesn't fix this on its own.

This should make the sysimage more resistant to invalidation (checking
rn).

Author: nsajko

src/LinearAlgebra.jl

@@ -750,7 +750,7 @@ of the problem that is solved on each processor.
     This function requires at least Julia 1.1. In Julia 1.0 it is available from
     the standard library `InteractiveUtils`.
 """
-function peakflops(n::Integer=4096; eltype::DataType=Float64, ntrials::Integer=3, parallel::Bool=false)
+function peakflops(n::Integer=4096; ::Type{eltype} = Float64, ntrials::Integer=3, parallel::Bool=false) where {eltype}
     t = zeros(Float64, ntrials)
     for i=1:ntrials
         a = ones(eltype,n,n)