update-checkout-config.json: Compiling Swift from source is a bad experience for new users if they are lacking ninja in $PATH. We have the code to automatically build ninja, so this patch clones the ``ninja-build/ninja`` repository as part of the checkout script.
update-checkout-config.json: Compiling Swift from source is a bad
experience for new users if they are lacking ninja in $PATH. We have the
code to automatically build ninja, so this patch clones the
``ninja-build/ninja`` repository as part of the checkout script.

Without this patch, if ninja is not installed on macOS or Linux (default = not
installed) and if you ``utils/update-checkout --clone``, it will not grab the
ninja project from github. Then ``utils/build-script``, not finding ninja in
$PATH, will try to build from source and complain about a missing ninja
repository and quit.

Some options are:
1) Change the message from ``swift-source/swift/utils/build-script: fatal error: can't find
source directory for ninja (tried swift-source/ninja)`` to ``Please
install or clone the ninja repository from github.`` This is not
friendly and asks the user to intervene manually for what we already
have code to automate.

2) Do a checkout of the ``ninja-build/ninja`` repository from github to the
``release`` branch when ``update-checkout`` runs and build it from
source if it's not found in $PATH. (This patch!)

3) Have users clone from ``apple/swift-ninja``.
This is not ideal because we have to maintain another repository without
any extra patches to ninja.

Fixes JIRA https://bugs.swift.org/browse/SR-3664

tjw/swift,shajrawi/swift,ahoppen/swift,stephentyrone/swift,codestergit/swift,codestergit/swift,practicalswift/swift,codestergit/swift,tkremenek/swift,jtbandes/swift,harlanhaskins/swift,shahmishal/swift,atrick/swift,bitjammer/swift,arvedviehweger/swift,arvedviehweger/swift,danielmartin/swift,JGiola/swift,frootloops/swift,nathawes/swift,glessard/swift,Jnosh/swift,JGiola/swift,uasys/swift,codestergit/swift,manavgabhawala/swift,arvedviehweger/swift,codestergit/swift,huonw/swift,gregomni/swift,uasys/swift,JaSpa/swift,huonw/swift,calebd/swift,amraboelela/swift,frootloops/swift,gribozavr/swift,apple/swift,amraboelela/swift,gottesmm/swift,xwu/swift,shajrawi/swift,natecook1000/swift,manavgabhawala/swift,manavgabhawala/swift,frootloops/swift,stephentyrone/swift,felix91gr/swift,natecook1000/swift,sschiau/swift,amraboelela/swift,deyton/swift,benlangmuir/swift,tinysun212/swift-windows,gottesmm/swift,CodaFi/swift,austinzheng/swift,huonw/swift,stephentyrone/swift,jckarter/swift,tjw/swift,airspeedswift/swift,rudkx/swift,shajrawi/swift,tardieu/swift,shahmishal/swift,jckarter/swift,deyton/swift,Jnosh/swift,brentdax/swift,lorentey/swift,OscarSwanros/swift,airspeedswift/swift,jopamer/swift,CodaFi/swift,hooman/swift,gottesmm/swift,karwa/swift,alblue/swift,apple/swift,natecook1000/swift,jmgc/swift,parkera/swift,deyton/swift,shajrawi/swift,parkera/swift,gribozavr/swift,swiftix/swift,frootloops/swift,parkera/swift,amraboelela/swift,atrick/swift,airspeedswift/swift,danielmartin/swift,hooman/swift,xedin/swift,jopamer/swift,gribozavr/swift,uasys/swift,aschwaighofer/swift,devincoughlin/swift,karwa/swift,JGiola/swift,tkremenek/swift,rudkx/swift,hughbe/swift,parkera/swift,OscarSwanros/swift,hughbe/swift,practicalswift/swift,tkremenek/swift,shahmishal/swift,jmgc/swift,jtbandes/swift,practicalswift/swift,CodaFi/swift,xedin/swift,brentdax/swift,nathawes/swift,zisko/swift,return/swift,calebd/swift,shajrawi/swift,ahoppen/swift,swiftix/swift,jopamer/swift,stephentyrone/swift,calebd/swift,xedin/swift,milseman/swift,JGiola/swift,airspeedswift/swift,brentdax/swift,harlanhaskins/swift,aschwaighofer/swift,xwu/swift,JaSpa/swift,hooman/swift,milseman/swift,Jnosh/swift,roambotics/swift,devincoughlin/swift,natecook1000/swift,glessard/swift,JGiola/swift,danielmartin/swift,bitjammer/swift,nathawes/swift,OscarSwanros/swift,tardieu/swift,hughbe/swift,felix91gr/swift,airspeedswift/swift,xwu/swift,bitjammer/swift,xedin/swift,uasys/swift,lorentey/swift,djwbrown/swift,return/swift,jckarter/swift,zisko/swift,gottesmm/swift,devincoughlin/swift,tinysun212/swift-windows,calebd/swift,xedin/swift,karwa/swift,benlangmuir/swift,JGiola/swift,calebd/swift,danielmartin/swift,swiftix/swift,atrick/swift,rudkx/swift,harlanhaskins/swift,zisko/swift,brentdax/swift,felix91gr/swift,xwu/swift,aschwaighofer/swift,CodaFi/swift,Jnosh/swift,alblue/swift,manavgabhawala/swift,calebd/swift,shahmishal/swift,lorentey/swift,ahoppen/swift,glessard/swift,apple/swift,rudkx/swift,bitjammer/swift,parkera/swift,alblue/swift,gregomni/swift,stephentyrone/swift,sschiau/swift,deyton/swift,hughbe/swift,tjw/swift,amraboelela/swift,gottesmm/swift,allevato/swift,OscarSwanros/swift,nathawes/swift,karwa/swift,natecook1000/swift,shajrawi/swift,allevato/swift,sschiau/swift,return/swift,atrick/swift,lorentey/swift,tardieu/swift,gregomni/swift,karwa/swift,CodaFi/swift,bitjammer/swift,nathawes/swift,tkremenek/swift,arvedviehweger/swift,bitjammer/swift,zisko/swift,tinysun212/swift-windows,ahoppen/swift,return/swift,jopamer/swift,alblue/swift,austinzheng/swift,jckarter/swift,jmgc/swift,OscarSwanros/swift,Jnosh/swift,JaSpa/swift,gribozavr/swift,aschwaighofer/swift,hooman/swift,uasys/swift,felix91gr/swift,parkera/swift,frootloops/swift,JaSpa/swift,devincoughlin/swift,sschiau/swift,shahmishal/swift,roambotics/swift,allevato/swift,harlanhaskins/swift,amraboelela/swift,harlanhaskins/swift,JaSpa/swift,jtbandes/swift,calebd/swift,karwa/swift,practicalswift/swift,roambotics/swift,xwu/swift,jmgc/swift,shajrawi/swift,djwbrown/swift,jtbandes/swift,devincoughlin/swift,practicalswift/swift,benlangmuir/swift,lorentey/swift,swiftix/swift,danielmartin/swift,tardieu/swift,devincoughlin/swift,practicalswift/swift,tinysun212/swift-windows,roambotics/swift,brentdax/swift,alblue/swift,frootloops/swift,hooman/swift,shahmishal/swift,danielmartin/swift,allevato/swift,felix91gr/swift,tardieu/swift,gregomni/swift,milseman/swift,harlanhaskins/swift,manavgabhawala/swift,deyton/swift,devincoughlin/swift,shajrawi/swift,OscarSwanros/swift,rudkx/swift,gottesmm/swift,return/swift,djwbrown/swift,djwbrown/swift,felix91gr/swift,sschiau/swift,zisko/swift,codestergit/swift,zisko/swift,sschiau/swift,atrick/swift,austinzheng/swift,tinysun212/swift-windows,glessard/swift,codestergit/swift,CodaFi/swift,gribozavr/swift,natecook1000/swift,tjw/swift,airspeedswift/swift,practicalswift/swift,hughbe/swift,jopamer/swift,manavgabhawala/swift,sschiau/swift,apple/swift,allevato/swift,milseman/swift,shahmishal/swift,hooman/swift,tjw/swift,natecook1000/swift,huonw/swift,manavgabhawala/swift,benlangmuir/swift,milseman/swift,ahoppen/swift,tkremenek/swift,nathawes/swift,atrick/swift,brentdax/swift,tkremenek/swift,lorentey/swift,apple/swift,frootloops/swift,devincoughlin/swift,jckarter/swift,arvedviehweger/swift,austinzheng/swift,tjw/swift,xedin/swift,return/swift,austinzheng/swift,parkera/swift,stephentyrone/swift,xwu/swift,jopamer/swift,jmgc/swift,hooman/swift,return/swift,benlangmuir/swift,milseman/swift,jtbandes/swift,lorentey/swift,tkremenek/swift,apple/swift,danielmartin/swift,gribozavr/swift,uasys/swift,xedin/swift,arvedviehweger/swift,jtbandes/swift,tinysun212/swift-windows,allevato/swift,brentdax/swift,karwa/swift,shahmishal/swift,jtbandes/swift,parkera/swift,lorentey/swift,swiftix/swift,Jnosh/swift,aschwaighofer/swift,gregomni/swift,gottesmm/swift,zisko/swift,rudkx/swift,austinzheng/swift,xedin/swift,jmgc/swift,jckarter/swift,alblue/swift,huonw/swift,tardieu/swift,aschwaighofer/swift,stephentyrone/swift,JaSpa/swift,gregomni/swift,jopamer/swift,nathawes/swift,swiftix/swift,glessard/swift,felix91gr/swift,ahoppen/swift,gribozavr/swift,milseman/swift,jckarter/swift,tjw/swift,austinzheng/swift,djwbrown/swift,tardieu/swift,djwbrown/swift,airspeedswift/swift,djwbrown/swift,alblue/swift,Jnosh/swift,xwu/swift,harlanhaskins/swift,roambotics/swift,JaSpa/swift,uasys/swift,sschiau/swift,OscarSwanros/swift,bitjammer/swift,aschwaighofer/swift,glessard/swift,allevato/swift,benlangmuir/swift,deyton/swift,deyton/swift,arvedviehweger/swift,amraboelela/swift,swiftix/swift,hughbe/swift,tinysun212/swift-windows,CodaFi/swift,practicalswift/swift,gribozavr/swift,jmgc/swift,hughbe/swift,roambotics/swift,huonw/swift,karwa/swift,huonw/swift