Fix reported bug #374 pow(x,INT_MIN) hangs - again


git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6439 4407c894-4637-0410-b4f5-ada5f102cad1
Merging r6297 through r6439 into 'stable/v3.x/mingw-w64-crt/math/powi.def.h'

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6440 4407c894-4637-0410-b4f5-ada5f102cad1
Merging r6414 through r6440 into 'stable/v3.x/mingw-w64-libraries/winpthreads'

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6441 4407c894-4637-0410-b4f5-ada5f102cad1