Link libdl as interface library

[masterleinad]

Fixes #4824. Basically, this just uses -ldl instead of the full library path for linking but we still try to find the library and add the include path for dlfcn.h.
An alternative to changing ${NAME}_FOUND_LIBRARIES for interface libraries, would be to not provide the library name in the initial call but add ${CMAKE_DL_LIBS} via target_link_libraries later.
I opted for the current approach since it feels less of a workaround, and interface libraries are not supposed to depend on hardcoded library paths anyway.

[nmm0]

Looks good to me. I think it's better to link the library like you did rather than adding yet another code path in the cmake

[dalg24]

I don't fully understand how specifying the INTERFACE dependency type helped. Are we abusing the current find TPL implementation? Why would it not yield the same link flag as w/o it?

[dalg24]

Why LIBRARY -> LIBRARIES?

[masterleinad]

This required fewer changes. KOKKOS_CREATE_IMPORTED_TPL (called by KOKKOS_FIND_IMPORTED) treats LIBRARY(referenced as TPL_LIBRARY) as IMPORTED_LOCATION but uses TARGET_LINK_LIBRARIES for LIBRARIES (referenced as TPL_LINK_LIBRARIES). In particular, we currently error out if KOKKOS_CREATE_IMPORTED_TPL called for an interface library gets a LIBRARY argument passed.

[masterleinad]

I don't fully understand how specifying the INTERFACE dependency type helped.

Without INTERFACE, we try to create an imported target that needs an imported location (otherwise you get a lot of CMake warnings) and this is precisely what we try to avoid here, also see

kokkos/cmake/kokkos_functions.cmake

Lines 309 to 370 in d19aab9

	MACRO(kokkos_create_imported_tpl NAME)
	CMAKE_PARSE_ARGUMENTS(TPL
	"INTERFACE"
	"LIBRARY"
	"LINK_LIBRARIES;INCLUDES;COMPILE_DEFINITIONS;COMPILE_OPTIONS;LINK_OPTIONS"
	${ARGN})
	IF (KOKKOS_HAS_TRILINOS)
	#TODO: we need to set a bunch of cache variables here
	ELSEIF (TPL_INTERFACE)
	ADD_LIBRARY(${NAME} INTERFACE)
	#Give this an importy-looking name
	ADD_LIBRARY(Kokkos::${NAME} ALIAS ${NAME})
	IF (TPL_LIBRARY)
	MESSAGE(SEND_ERROR "TPL Interface library ${NAME} should not have an IMPORTED_LOCATION")
	ENDIF()
	#Things have to go in quoted in case we have multiple list entries
	IF(TPL_LINK_LIBRARIES)
	TARGET_LINK_LIBRARIES(${NAME} INTERFACE ${TPL_LINK_LIBRARIES})
	ENDIF()
	IF(TPL_INCLUDES)
	TARGET_INCLUDE_DIRECTORIES(${NAME} INTERFACE ${TPL_INCLUDES})
	ENDIF()
	IF(TPL_COMPILE_DEFINITIONS)
	TARGET_COMPILE_DEFINITIONS(${NAME} INTERFACE ${TPL_COMPILE_DEFINITIONS})
	ENDIF()
	IF(TPL_COMPILE_OPTIONS)
	TARGET_COMPILE_OPTIONS(${NAME} INTERFACE ${TPL_COMPILE_OPTIONS})
	ENDIF()
	IF(TPL_LINK_OPTIONS)
	TARGET_LINK_LIBRARIES(${NAME} INTERFACE ${TPL_LINK_OPTIONS})
	ENDIF()
	ELSE()
	ADD_LIBRARY(${NAME} UNKNOWN IMPORTED)
	IF(TPL_LIBRARY)
	SET_TARGET_PROPERTIES(${NAME} PROPERTIES
	IMPORTED_LOCATION ${TPL_LIBRARY})
	ENDIF()
	#Things have to go in quoted in case we have multiple list entries
	IF(TPL_LINK_LIBRARIES)
	SET_TARGET_PROPERTIES(${NAME} PROPERTIES
	INTERFACE_LINK_LIBRARIES "${TPL_LINK_LIBRARIES}")
	ENDIF()
	IF(TPL_INCLUDES)
	SET_TARGET_PROPERTIES(${NAME} PROPERTIES
	INTERFACE_INCLUDE_DIRECTORIES "${TPL_INCLUDES}")
	ENDIF()
	IF(TPL_COMPILE_DEFINITIONS)
	SET_TARGET_PROPERTIES(${NAME} PROPERTIES
	INTERFACE_COMPILE_DEFINITIONS "${TPL_COMPILE_DEFINITIONS}")
	ENDIF()
	IF(TPL_COMPILE_OPTIONS)
	SET_TARGET_PROPERTIES(${NAME} PROPERTIES
	INTERFACE_COMPILE_OPTIONS "${TPL_COMPILE_OPTIONS}")
	ENDIF()
	IF(TPL_LINK_OPTIONS)
	SET_TARGET_PROPERTIES(${NAME} PROPERTIES
	INTERFACE_LINK_LIBRARIES "${TPL_LINK_OPTIONS}")
	ENDIF()
	ENDIF()
	ENDMACRO()

[cz4rs]

This required fewer changes. KOKKOS_CREATE_IMPORTED_TPL (called by KOKKOS_FIND_IMPORTED) treats LIBRARY(referenced as TPL_LIBRARY) as IMPORTED_LOCATION but uses TARGET_LINK_LIBRARIES for LIBRARIES (referenced as TPL_LINK_LIBRARIES). In particular, we currently error out if KOKKOS_CREATE_IMPORTED_TPL called for an interface library gets a LIBRARY argument passed.

Ok, so the difference between passing LIBRARY and LIBRARIES is somewhat surprising. The documentation for the macro doesn't really help:

kokkos/cmake/kokkos_functions.cmake

Lines 632 to 638 in 86af51d

	# ``LIBRARY <name>``
	#
	# If specified, this gives the name of the library to look for
	#
	# ``LIBRARIES <name1> <name2> ...``
	#
	# If specified, this gives a list of libraries to find for the package

And if I didn't look at the implementation, I would intuitively expect something like:

  FOREACH(LIB ${TPL_LIBRARIES})
    do-the-same-stuff-we-do-for-single-library()
  ENDFOREACH()

[cz4rs]

Looks good to me!