[CMake] Using -DOPTION="something=moof" mangles the OPTION value to "something:UNINITIALIZED=moof"

[Marcus Fritzsch]

I discovered this behavior on my ubuntu 11.04 amd64 workstation with
cmake 2.8.3 when trying to set an -march= option for gcc:

    cmake -DCMAKE_C_FLAGS="-Os -march=native -flto
-freorder-blocks-and-partition" ....

was mangled to be

    CMAKE_C_FLAGS=-Os -march:UNINITIALIZED=native -flto
-freorder-blocks-and-partition

in the CMakeCache.txt.

I haven't had much luck with the search engine of my choice finding
anything on the issue.