BLD: Avoid using os.spawnve in favor of os.spawnv in exec_command
BLD: Avoid using os.spawnve in favor of os.spawnv in exec_command

The env modifying spawn* function are not thread safe on windows (python
issue6476) so avoid using them unless so requested by the caller.

References #7607

maniteja123/numpy,SiccarPoint/numpy,madphysicist/numpy,joferkington/numpy,Eric89GXL/numpy,mhvk/numpy,skwbc/numpy,kiwifb/numpy,mattip/numpy,madphysicist/numpy,joferkington/numpy,abalkin/numpy,MSeifert04/numpy,endolith/numpy,MSeifert04/numpy,MSeifert04/numpy,rgommers/numpy,pdebuyl/numpy,chatcannon/numpy,anntzer/numpy,njase/numpy,jorisvandenbossche/numpy,simongibbons/numpy,stuarteberg/numpy,kiwifb/numpy,endolith/numpy,numpy/numpy,bertrand-l/numpy,ahaldane/numpy,chatcannon/numpy,charris/numpy,abalkin/numpy,pdebuyl/numpy,gfyoung/numpy,bringingheavendown/numpy,AustereCuriosity/numpy,ahaldane/numpy,shoyer/numpy,Eric89GXL/numpy,seberg/numpy,jorisvandenbossche/numpy,simongibbons/numpy,shoyer/numpy,pizzathief/numpy,Eric89GXL/numpy,seberg/numpy,numpy/numpy,simongibbons/numpy,charris/numpy,ddasilva/numpy,tynn/numpy,ddasilva/numpy,grlee77/numpy,ContinuumIO/numpy,seberg/numpy,bertrand-l/numpy,b-carter/numpy,rgommers/numpy,simongibbons/numpy,tacaswell/numpy,utke1/numpy,behzadnouri/numpy,bringingheavendown/numpy,jorisvandenbossche/numpy,WarrenWeckesser/numpy,pbrod/numpy,behzadnouri/numpy,jakirkham/numpy,stuarteberg/numpy,maniteja123/numpy,WarrenWeckesser/numpy,skwbc/numpy,ssanderson/numpy,ssanderson/numpy,utke1/numpy,shoyer/numpy,chatcannon/numpy,WarrenWeckesser/numpy,jorisvandenbossche/numpy,jakirkham/numpy,gmcastil/numpy,jorisvandenbossche/numpy,seberg/numpy,mhvk/numpy,stuarteberg/numpy,shoyer/numpy,madphysicist/numpy,ssanderson/numpy,njase/numpy,bringingheavendown/numpy,dwillmer/numpy,mhvk/numpy,SiccarPoint/numpy,pdebuyl/numpy,ddasilva/numpy,pbrod/numpy,charris/numpy,stuarteberg/numpy,solarjoe/numpy,shoyer/numpy,madphysicist/numpy,ahaldane/numpy,pizzathief/numpy,skwbc/numpy,utke1/numpy,pbrod/numpy,joferkington/numpy,numpy/numpy,rgommers/numpy,gmcastil/numpy,tacaswell/numpy,b-carter/numpy,tynn/numpy,b-carter/numpy,jakirkham/numpy,AustereCuriosity/numpy,anntzer/numpy,MSeifert04/numpy,dwillmer/numpy,WarrenWeckesser/numpy,tynn/numpy,dwillmer/numpy,mhvk/numpy,pizzathief/numpy,charris/numpy,grlee77/numpy,anntzer/numpy,grlee77/numpy,MSeifert04/numpy,bertrand-l/numpy,ahaldane/numpy,gmcastil/numpy,njase/numpy,AustereCuriosity/numpy,madphysicist/numpy,gfyoung/numpy,WarrenWeckesser/numpy,Eric89GXL/numpy,behzadnouri/numpy,pizzathief/numpy,SiccarPoint/numpy,pbrod/numpy,endolith/numpy,ContinuumIO/numpy,tacaswell/numpy,grlee77/numpy,mattip/numpy,kiwifb/numpy,ContinuumIO/numpy,endolith/numpy,pdebuyl/numpy,numpy/numpy,ahaldane/numpy,abalkin/numpy,solarjoe/numpy,joferkington/numpy,mattip/numpy,jakirkham/numpy,simongibbons/numpy,jakirkham/numpy,gfyoung/numpy,mattip/numpy,solarjoe/numpy,pbrod/numpy,mhvk/numpy,SiccarPoint/numpy,dwillmer/numpy,maniteja123/numpy,pizzathief/numpy,rgommers/numpy,anntzer/numpy,grlee77/numpy