Fix command case

git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@24918 dab4d1a6-ed17-0410-a064-d1ae371a2980
Add MINGW check

Tested: MinGW on Windows 7

git-svn-id: https://svn.hdfgroup.uiuc.edu/hdf5/trunk@24919 dab4d1a6-ed17-0410-a064-d1ae371a2980