Add new sparse matmul performance tracking test

Existing test for sparse matrix-matrix multiplication is not very representative
Tweaks for cross compiling from Cygwin to MinGW

* Cygwin versions of MinGW compilers put standard libraries in /bin, not /lib
* Blas and Lapack should be in build_shlibdir
* Don't use wine for Cygwin to MinGW cross compile
* New cygpath_w helper function to convert Cygwin paths to Windows-style so MinGW-compiled
executables can understand them
* Use cygpath_w for system image file locations
Fix doc example of @test_approx_eq_eps precision argument 

`e-2` means Euler's number minus two. I guess original author wanted to mean `10^-2`
Merge pull request #5968 from cdsousa/patch-1

Fix doc example of @test_approx_eq_eps precision argument
fix #5963
Merge pull request #5922 from tkelman/patch-1

Add new sparse matmul performance tracking test
Merge pull request #5965 from tkelman/cygwin-to-mingw-cross

RFC: Allow Cygwin to MinGW cross compilation