CI: making build parallel

Adding -k -j8 on MacOS.
Moving from NMake to Ninja on Windows.
8 jobs for master in 4 minutes and 37 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Configure
passed #4116
mac
configure:mac

00:00:40

passed #4117
windows
configure:win32

00:00:40

 
  Build
passed #4119
mac
build:mac

00:02:32

passed #4118
windows
build:win32

00:02:43

 
  Dist
passed #4121
mac
dist:mac

00:00:24

passed #4120
windows
dist:win32

00:00:31

 
  Pack
passed #4123
mac
pack:mac

00:00:36

passed #4122
windows
pack:win32

00:00:39