[CMake] How the heck does one set options?

[Dan Kegel]

Right, so, I have this fragment:

set(gtest_force_shared_crt ON)
add_subdirectory(gtest)

Oddly, when I run cmake, that variable is off.  WTF?

Looking at the cache, I see

build/CMakeCache.txt:gtest_force_shared_crt:BOOL=OFF

It looks like someone else ran into this before,
http://www.mail-archive.com/cmake@cmake.org/msg20930.html

What am I missing?  Surely it can't be this hard to set options...
- Dan