custom function for build step

[smanders]

there are times when it would be cleaner to specify a cmake function for the build step...

currently, a build step function has to match a proper naming format

• https://github.com/smanders/externpro/blob/18.01.1/modules/macpro.cmake#L179-L182

# build
if(COMMAND build_${cmdp})
  file(APPEND ${stepBuild} "build_${cmdp}()\n")
endif()

where cmdp comes from the name of the project, with - and . replaced with _

• https://github.com/smanders/externpro/blob/18.01.1/modules/macpro.cmake#L156-L159

get_filename_component(pro ${proj} NAME)
string(REPLACE ".cmake" "" pro ${pro}) # name w/o .cmake extension
string(REPLACE "-" "_" cmdp ${pro})
string(REPLACE "." "_" cmdp ${cmdp})

which means that a build-step function for ffmpeg_2.6.2.cmake https://github.com/smanders/externpro/blob/18.01.1/projects/ffmpeg_2.6.2.cmake would need to be build_ffmpeg_2_6_2()

• if the version of ffmpeg is updated one would need to remember to also change the build function name and the required underscores are also ugly and hard to remember

not ideal -- and the reason I currently build multiple versions of ffmpeg from one build-step function https://github.com/smanders/externpro/blob/18.01.1/projects/ffmpeg.cmake#L36

• which is also not ideal, especially given how different it currently is to build ffmpeg 2.6.2 and 2.6.2.1...

it would be more convenient (and something I will use to build glew) to specify the cmake function for the build step with a BUILD_FUNC argument in the PRO_${PRO} variable that is defined for each project

[smanders]

completed with commit to dev branch referenced above

[smanders]

examples of using custom BUILD_FUNC

• externpro/projects/glew_1.13.0.cmake

  Lines 22 to 25 in 2e71eea

  	BUILD_FUNC build_glew_bldver
  	)
  	########################################
  	function(build_glew_bldver)

• externpro/projects/glew_1.7.0.cmake

  Lines 21 to 24 in 2e71eea

  	BUILD_FUNC build_glew_mswver
  	)
  	########################################
  	function(build_glew_mswver)