cmake: use Ninja by default

This changes the cmake class to use Ninja instead of Make by default.

If a recipe is broken with Ninja then the recipe can set OECMAKE_GENERATOR="Unix
Makefiles" to change back to Make.

(From OE-Core rev: bacaa26decb8a1e3fa672e1923954793fde48766)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/cmake.bbclass

@@ -9,7 +9,7 @@ CCACHE = ""
 
 # What CMake generator to use.
 # The supported options are "Unix Makefiles" or "Ninja".
-OECMAKE_GENERATOR ?= "Unix Makefiles"
+OECMAKE_GENERATOR ?= "Ninja"
 
 python() {
     generator = d.getVar("OECMAKE_GENERATOR")