Make auto-reconfiguring work if CFLAGS contains more than one flag.
Make auto-reconfiguring work if CFLAGS contains more than one flag.

When using an open-source clang on OS X, one has to pass an isysroot
flag so that it can find system headers (stdio.h), like so:

  CXX=path/to/clang++ CFLAGS="-isysroot $(xcrun -show-sdk-path)" ./configure.py

Previously, configure.py wouldn't quote envvars containing spaces, so
it'd rerun this as

  CXX=path/to/clang++ CFLAGS=-isysroot /sysroot/path ./configure.py

which would then die because /sysroot/path wasn't excecutable.

ndsol/subninja,autopulated/ninja,juntalis/ninja,hnney/ninja,dendy/ninja,ilor/ninja,atetubou/ninja,vvvrrooomm/ninja,bradking/ninja,bmeurer/ninja,maruel/ninja,hnney/ninja,rjogrady/ninja,jendrikillner/ninja,mgaunard/ninja,nicolasdespres/ninja,metti/ninja,colincross/ninja,nafest/ninja,ndsol/subninja,Maratyszcza/ninja-pypi,automeka/ninja,sxlin/dist_ninja,moroten/ninja,vvvrrooomm/ninja,mohamed/ninja,hnney/ninja,sxlin/dist_ninja,rjogrady/ninja,lizh06/ninja,sxlin/dist_ninja,Ju2ender/ninja,mydongistiny/ninja,liukd/ninja,automeka/ninja,ilor/ninja,jendrikillner/ninja,bmeurer/ninja,maruel/ninja,Ju2ender/ninja,Maratyszcza/ninja-pypi,synaptek/ninja,sgraham/ninja,ctiller/ninja,Maratyszcza/ninja-pypi,dorgonman/ninja,juntalis/ninja,sxlin/dist_ninja,ninja-build/ninja,ninja-build/ninja,Qix-/ninja,vvvrrooomm/ninja,tfarina/ninja,bradking/ninja,nicolasdespres/ninja,atetubou/ninja,bmeurer/ninja,mgaunard/ninja,jimon/ninja,bradking/ninja,sgraham/ninja,ignatenkobrain/ninja,kissthink/ninja,autopulated/ninja,bmeurer/ninja,nico/ninja,Ju2ender/ninja,moroten/ninja,jendrikillner/ninja,iwadon/ninja,ignatenkobrain/ninja,ilor/ninja,sgraham/ninja,sgraham/ninja,jendrikillner/ninja,atetubou/ninja,ignatenkobrain/ninja,atetubou/ninja,autopulated/ninja,ThiagoGarciaAlves/ninja,dorgonman/ninja,AoD314/ninja,martine/ninja,martine/ninja,nico/ninja,AoD314/ninja,maruel/ninja,metti/ninja,moroten/ninja,kissthink/ninja,Qix-/ninja,synaptek/ninja,colincross/ninja,mydongistiny/ninja,ignatenkobrain/ninja,tfarina/ninja,jimon/ninja,dendy/ninja,rjogrady/ninja,moroten/ninja,colincross/ninja,Maratyszcza/ninja-pypi,ninja-build/ninja,metti/ninja,fuchsia-mirror/third_party-ninja,dorgonman/ninja,ndsol/subninja,dendy/ninja,ThiagoGarciaAlves/ninja,mohamed/ninja,Qix-/ninja,mgaunard/ninja,ndsol/subninja,nicolasdespres/ninja,lizh06/ninja,jimon/ninja,mohamed/ninja,tfarina/ninja,liukd/ninja,ctiller/ninja,kissthink/ninja,sxlin/dist_ninja,maruel/ninja,ThiagoGarciaAlves/ninja,autopulated/ninja,bradking/ninja,ilor/ninja,lizh06/ninja,rjogrady/ninja,martine/ninja,metti/ninja,AoD314/ninja,vvvrrooomm/ninja,Ju2ender/ninja,nico/ninja,ctiller/ninja,sxlin/dist_ninja,automeka/ninja,liukd/ninja,fuchsia-mirror/third_party-ninja,juntalis/ninja,ThiagoGarciaAlves/ninja,lizh06/ninja,mgaunard/ninja,kissthink/ninja,juntalis/ninja,liukd/ninja,sxlin/dist_ninja,nico/ninja,synaptek/ninja,mohamed/ninja,automeka/ninja,ctiller/ninja,nafest/ninja,synaptek/ninja,iwadon/ninja,tfarina/ninja,mydongistiny/ninja,mydongistiny/ninja,hnney/ninja,dendy/ninja,fuchsia-mirror/third_party-ninja,nicolasdespres/ninja,AoD314/ninja,Qix-/ninja,fuchsia-mirror/third_party-ninja,nafest/ninja,martine/ninja,ninja-build/ninja,iwadon/ninja,nafest/ninja,dorgonman/ninja,jimon/ninja,colincross/ninja,iwadon/ninja