In CMake, how do I work around the Debug and Release directories Visual Studio 2010 tries to add?

It depends a bit on what you want precisely, but I would recommend to take a look at the available target properties, similar to this question.

It depends a bit on what you want exactly. For each target, you could manually set the library_output_directory or runtime_output_directory properties.

if ( MSVC )
    set_target_properties( ${targetname} PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${youroutputdirectory} )
    set_target_properties( ${targetname} PROPERTIES LIBRARY_OUTPUT_DIRECTORY_DEBUG ${youroutputdirectory} )
    set_target_properties( ${targetname} PROPERTIES LIBRARY_OUTPUT_DIRECTORY_RELEASE ${youroutputdirectory} )
    # etc for the other available configuration types (MinSizeRel, RelWithDebInfo)
endif ( MSVC )

You could also do this globally for all sub-projects, using something like this:

# First for the generic no-config case (e.g. with mingw)
set( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${youroutputdirectory} )
set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${youroutputdirectory} )
set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${youroutputdirectory} )
# Second, for multi-config builds (e.g. msvc)
foreach( OUTPUTCONFIG ${CMAKE_CONFIGURATION_TYPES} )
    string( TOUPPER ${OUTPUTCONFIG} OUTPUTCONFIG )
    set( CMAKE_RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${youroutputdirectory} )
    set( CMAKE_LIBRARY_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${youroutputdirectory} )
    set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${youroutputdirectory} )
endforeach( OUTPUTCONFIG CMAKE_CONFIGURATION_TYPES )

In current versions of CMake you can use a generator expression for LIBRARY_OUTPUT_DIRECTORY to avoid the configuration-specific suffix.

I just added $<$<CONFIG:Debug>:>, which always expands to nothing, to mine. This looks a bit weird, but it does work, and it's not so weird you can't explain it with a brief comment:

# Use a generator expression so that the specified folder is used directly, without any
# configuration-dependent suffix.
#
# See https://cmake.org/cmake/help/v3.8/prop_tgt/LIBRARY_OUTPUT_DIRECTORY.html
set_target_properties(library PROPERTIES
                      LIBRARY_OUTPUT_DIRECTORY my/folder/$<$<CONFIG:Debug>:>)

https://cmake.org/cmake/help/latest/prop_tgt/LIBRARY_OUTPUT_DIRECTORY.html explains that:

Multi-configuration generators (VS, Xcode) append a per-configuration subdirectory to the specified directory unless a generator expression is used.

Thus, the only workaround is to use a generator expression. One cool way to do it is by using $<0:> at the end of your path. So if your path is /what/ever/, you will need to replace it with /what/ever/$<0:>.

Example with the target: Nuua and the path: C:/Nuua/bin/

set_target_properties(nuua PROPERTIES RUNTIME_OUTPUT_DIRECTORY C:/Nuua/bin/$<0:>)