tools/cmake: add MAKE config variable

Makes sure that Ninja from staging_dir is used and nowhere else.

Reported by reproducible builds project. Builds have been failing ever
since tools/cmake started using Ninja.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

tools/cmake/Makefile

@@ -25,7 +25,8 @@ HOST_CONFIGURE_VARS += \
 	CC="$(HOSTCC_NOCACHE)" \
 	CXX="$(HOSTCXX_NOCACHE)" \
 	MAKEFLAGS="$(HOST_JOBS)" \
-	CXXFLAGS="$(HOST_CFLAGS)"
+	CXXFLAGS="$(HOST_CFLAGS)" \
+	MAKE="$(STAGING_DIR_HOST)/bin/ninja"
 
 HOST_CONFIGURE_ARGS := \
 	$(if $(MAKE_JOBSERVER),--parallel="$(MAKE_JOBSERVER)") \