otfcc: build with ninja

Makefiles generated by premake do not support parallel building:

cd build/gmake
make -f deps.make config=release_x64 obj/x64/release/deps/sds.o
sds.c
../../dep/extern/sds.c:1088:1: fatal error: opening dependency file obj/x64/release/deps/sds.d: No such file or directory
 }
 ^
compilation terminated.
make: *** [deps.make:194: obj/x64/release/deps/sds.o] Error 1