[CMake] Passing CMake verbosity down to external project

[Bill Somerville]

Hi All,

I have an ExternalProject_Add() that uses autotools and I want to tell 
it to do a verbose make when my CMake parent project has been invoked 
with VERBOSE=1 or CMAKE_VERBOSE_MAKEFILE=ON. The external project 
requires V=1 as a make argument to do this.

How do I detect the request for verbose make in my CMakeLists.txt so I 
can translate it to V=1 in the BUILD_COMMAND of the 
ExternalProject_Add() function?

Regards
Bill Somerville.