TST: Respect compiler customizations
TST: Respect compiler customizations

Without calling `compiler.customize(None)` customizations using
environment variables like CC won't be honoured

ahaldane/numpy,jorisvandenbossche/numpy,simongibbons/numpy,pizzathief/numpy,jorisvandenbossche/numpy,mhvk/numpy,chatcannon/numpy,endolith/numpy,endolith/numpy,ahaldane/numpy,charris/numpy,ahaldane/numpy,seberg/numpy,rgommers/numpy,endolith/numpy,grlee77/numpy,jorisvandenbossche/numpy,MSeifert04/numpy,abalkin/numpy,anntzer/numpy,numpy/numpy,mattip/numpy,jakirkham/numpy,endolith/numpy,Eric89GXL/numpy,mhvk/numpy,bringingheavendown/numpy,numpy/numpy,jakirkham/numpy,gfyoung/numpy,pdebuyl/numpy,chatcannon/numpy,anntzer/numpy,pbrod/numpy,tynn/numpy,rgommers/numpy,jakirkham/numpy,mhvk/numpy,madphysicist/numpy,behzadnouri/numpy,ahaldane/numpy,ahaldane/numpy,behzadnouri/numpy,jorisvandenbossche/numpy,MSeifert04/numpy,simongibbons/numpy,pizzathief/numpy,mhvk/numpy,Eric89GXL/numpy,abalkin/numpy,madphysicist/numpy,madphysicist/numpy,Eric89GXL/numpy,simongibbons/numpy,WarrenWeckesser/numpy,solarjoe/numpy,pdebuyl/numpy,WarrenWeckesser/numpy,behzadnouri/numpy,shoyer/numpy,solarjoe/numpy,MSeifert04/numpy,rgommers/numpy,pizzathief/numpy,grlee77/numpy,anntzer/numpy,shoyer/numpy,shoyer/numpy,pbrod/numpy,bringingheavendown/numpy,seberg/numpy,WarrenWeckesser/numpy,MSeifert04/numpy,tynn/numpy,chatcannon/numpy,abalkin/numpy,WarrenWeckesser/numpy,grlee77/numpy,charris/numpy,pdebuyl/numpy,pbrod/numpy,shoyer/numpy,madphysicist/numpy,mhvk/numpy,seberg/numpy,b-carter/numpy,mattip/numpy,pizzathief/numpy,numpy/numpy,jakirkham/numpy,b-carter/numpy,pbrod/numpy,simongibbons/numpy,shoyer/numpy,jorisvandenbossche/numpy,madphysicist/numpy,simongibbons/numpy,bringingheavendown/numpy,charris/numpy,mattip/numpy,tynn/numpy,numpy/numpy,grlee77/numpy,seberg/numpy,gfyoung/numpy,pizzathief/numpy,anntzer/numpy,gfyoung/numpy,Eric89GXL/numpy,MSeifert04/numpy,WarrenWeckesser/numpy,solarjoe/numpy,mattip/numpy,pdebuyl/numpy,b-carter/numpy,pbrod/numpy,jakirkham/numpy,rgommers/numpy,charris/numpy,grlee77/numpy