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
Merge pull request #5965 from tkelman/cygwin-to-mingw-cross

RFC: Allow Cygwin to MinGW cross compilation
Update Brazilian Portuguese documentation link

For reasons similar to 096893a90.
Comment out test for balancing. Failing with LAPACK 3.5, because balancing has been improved.
Merge pull request #5976 from JuliaLang/anj/eigtest

Comment out test for balancing. Failing with LAPACK 3.5, because balancing has been improved.
Merge pull request #5974 from andrioni/patch-4

Update Brazilian Portuguese documentation link
Merge https://github.com/JuliaLang/julia into rjg/jstan