DOC: update toolchain.rst to reflect windows universal C runtime (#13713)
DOC: update toolchain.rst to reflect windows universal C runtime (#13713)

* small toolchain.rst fixes

* doc/toolchain: reflect changes that happened on wikipedia reference

* doc/toolchain: add note about optional pythran support

* doc/toolchain: add note about status of OpenMP support

* doc/toolchain: add overall compilers section & info on official builds

Also make the various compiler sections subsections of overall section.

* doc/toolchain: update 'C Compilers' section & reflect windows UCRT

* doc/toolchain: re-add/rewrite deleted paragraph for C/C++ standards

* respond to review feedback

* fix doc build errors/warnings
scipy/scipy,vigna/scipy,WarrenWeckesser/scipy,scipy/scipy,endolith/scipy,Stefan-Endres/scipy,andyfaff/scipy,matthew-brett/scipy,vigna/scipy,anntzer/scipy,tylerjereddy/scipy,Eric89GXL/scipy,anntzer/scipy,zerothi/scipy,zerothi/scipy,ilayn/scipy,rgommers/scipy,andyfaff/scipy,andyfaff/scipy,tylerjereddy/scipy,anntzer/scipy,WarrenWeckesser/scipy,e-q/scipy,tylerjereddy/scipy,rgommers/scipy,matthew-brett/scipy,grlee77/scipy,tylerjereddy/scipy,perimosocordiae/scipy,Stefan-Endres/scipy,grlee77/scipy,WarrenWeckesser/scipy,mdhaber/scipy,anntzer/scipy,perimosocordiae/scipy,Eric89GXL/scipy,Eric89GXL/scipy,WarrenWeckesser/scipy,e-q/scipy,matthew-brett/scipy,perimosocordiae/scipy,ilayn/scipy,rgommers/scipy,anntzer/scipy,ilayn/scipy,ilayn/scipy,perimosocordiae/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,perimosocordiae/scipy,andyfaff/scipy,tylerjereddy/scipy,endolith/scipy,zerothi/scipy,endolith/scipy,scipy/scipy,endolith/scipy,anntzer/scipy,vigna/scipy,zerothi/scipy,zerothi/scipy,Eric89GXL/scipy,grlee77/scipy,Eric89GXL/scipy,mdhaber/scipy,endolith/scipy,mdhaber/scipy,rgommers/scipy,ilayn/scipy,perimosocordiae/scipy,e-q/scipy,matthew-brett/scipy,vigna/scipy,WarrenWeckesser/scipy,mdhaber/scipy,scipy/scipy,Stefan-Endres/scipy,mdhaber/scipy,Eric89GXL/scipy,vigna/scipy,endolith/scipy,Stefan-Endres/scipy,ilayn/scipy,zerothi/scipy,mdhaber/scipy,WarrenWeckesser/scipy,matthew-brett/scipy,grlee77/scipy,e-q/scipy,grlee77/scipy,rgommers/scipy,scipy/scipy,andyfaff/scipy,e-q/scipy,andyfaff/scipy,scipy/scipy