build: Inherit -n and -jN flags if Ninja #12219

Makefile

@@ -58,11 +58,15 @@ endif
 
 BUILD_CMD = $(BUILD_TOOL)
 
-ifneq ($(VERBOSE),)
-  # Only need to handle Ninja here.  Make will inherit the VERBOSE variable.
-  ifeq ($(BUILD_TYPE),Ninja)
+# Only need to handle Ninja here.  Make will inherit the VERBOSE variable, and the -j and -n flags.
+ifeq ($(BUILD_TYPE),Ninja)
+  ifneq ($(VERBOSE),)
     BUILD_CMD += -v
   endif
+  BUILD_CMD += $(shell printf '%s' '$(MAKEFLAGS)' | grep -o -- '-j[0-9]\+')
+  ifeq (n,$(findstring n,$(firstword -$(MAKEFLAGS))))
+    BUILD_CMD += -n
+  endif
 endif
 
 DEPS_CMAKE_FLAGS ?=