create SIRF_DISABLE_Gadgetron etc

[KrisThielemans]

SIRF has CMake variables DISABLE_Gadgetron etc. Currently these are not exposed in External_SIRF.cmake. That means that they can only be set via SIRF_EXTRA_CMAKE_ARGS="-DDISABLE_Gadgetron:BOOL=OFF". (Similar variables are exposed in External_STIR.cmake).

To make matters confusing, there are BUILD_* variables in the Superbuild. There is some logic related to the BUILD_Gadgetron etc variables

SIRF-SuperBuild/SuperBuild/External_SIRF.cmake

Lines 28 to 39 in 02d30f8

	if (${BUILD_Gadgetron})
	set(${proj}_DEPENDENCIES "${${proj}_DEPENDENCIES};Gadgetron")
	endif()
	if (${BUILD_NIFTYREG})
	set(${proj}_DEPENDENCIES "${${proj}_DEPENDENCIES};NIFTYREG")
	endif()
	if (${BUILD_STIR})
	set(${proj}_DEPENDENCIES "${${proj}_DEPENDENCIES};STIR")
	endif()
	if (${BUILD_SPM})
	set(${proj}_DEPENDENCIES "${${proj}_DEPENDENCIES};SPM")
	endif()

This says that if you set BUILD_Gadgetron=OFF, Gadgetron is not added as a dependency to the SIRF project (the ExternalProject dependencies ensure build order). That is fine in itself, but it does NOT mean that the SIRF build will not look for ISMRMRD (and optionally Gadgetron toolboxes).

Note that on Windows, we set BUILD_Gadgetron=OFF such that we don't attempt to build Gadgetron, but Gadgetron support in SIRF is still enabled (by intention).

Conclusion

if you don't need MR support in SIRF, at present you need to

cmake -DBUILD_Gadgetron:BOOL=OFF -DSIRF_EXTRA_CMAKE_ARGS="-DDISABLE_Gadgetron:BOOL=OFF" ....

Not great...

More on naming

In addition, there are the USE_SYSTEM_* variables. You can set BUILD_Gadgetron=ON but USE_SYSTEM_Gadgetron=ON. which means that Gadgetron wll not be built. Confusing...

See some more discussion on naming in #511.