Backport 7908, BLD: Fixed MKL detection for recent versions of this library.

[charris]

Backport #7908.

The detection of the MKL library was broken. According to Intel, the recommended way to build numpy and use MKL is to define a site.cfg with the values:

library_dirs = /opt/intel/compilers_and_libraries_2016/linux/mkl/lib/intel64
include_dirs = /opt/intel/compilers_and_libraries_2016/linux/mkl/include
mkl_libs = mkl_rt
lapack_libs = 

See https://software.intel.com/en-us/articles/numpyscipy-with-intel-mkl for more info.

The name of the libraries in system_info has been updated so now no site.cfg is needed if the MKLROOT environment variable is properly set to detect MKL.