BUILD: makefile: also define cmd_CXX to pretty-print C++ build commands

Device Atlas' dummy lib will use a C++ file when built with cache
support, so for completeness we'll have to pretty-print it as well.
Let's define cmd_CXX.

include/make/verbose.mk

@@ -10,6 +10,7 @@ endif
 # or to themselves depending on the verbosity level.
 ifeq ($V,1)
 cmd_CC = $(CC)
+cmd_CXX = $(CXX)
 cmd_LD = $(LD)
 cmd_AR = $(AR)
 cmd_MAKE = +$(MAKE)
@@ -17,12 +18,14 @@ else
 ifeq (3.81,$(firstword $(sort $(MAKE_VERSION) 3.81)))
 # 3.81 or above
 cmd_CC = $(info $   CC      $@) $(Q)$(CC)
+cmd_CXX = $(info $   CXX     $@) $(Q)$(CXX)
 cmd_LD = $(info $   LD      $@) $(Q)$(LD)
 cmd_AR = $(info $   AR      $@) $(Q)$(AR)
 cmd_MAKE = $(info $   MAKE    $@) $(Q)+$(MAKE)
 else
 # 3.80 or older
 cmd_CC = $(Q)echo "  CC      $@";$(CC)
+cmd_CXX = $(Q)echo "  CXX     $@";$(CXX)
 cmd_LD = $(Q)echo "  LD      $@";$(LD)
 cmd_AR = $(Q)echo "  AR      $@";$(AR)
 cmd_MAKE = $(Q)echo "  MAKE    $@";$(MAKE)