Fixup interface libraries for JSON and XML libs.

thirdparty/NLohmannJson/CMakeLists.txt

-add_library(NLohmann::Json INTERFACE IMPORTED GLOBAL)
-set_target_properties(NLohmann::Json PROPERTIES
-  INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_CURRENT_SOURCE_DIR}/json/src
-)
+add_subdirectory(json)

thirdparty/NLohmannJson/json/CMakeLists.txt

+add_library(NLohmannJson INTERFACE)
+target_include_directories(NLohmannJson INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
+)
+install(TARGETS NLohmannJson EXPORT adios2Exports)

thirdparty/pugixml/CMakeLists.txt

-# This is an extremely simple and tiny library.  Rather than build it
-# seperately we'll just create an interface library containing the sources and
-# headers
-add_library(pugixml INTERFACE)
-target_sources(pugixml INTERFACE
-  ${CMAKE_CURRENT_SOURCE_DIR}/pugixml/src/pugiconfig.hpp
-  ${CMAKE_CURRENT_SOURCE_DIR}/pugixml/src/pugixml.hpp
-  ${CMAKE_CURRENT_SOURCE_DIR}/pugixml/src/pugixml.cpp
-)
-target_include_directories(pugixml INTERFACE
-  ${CMAKE_CURRENT_SOURCE_DIR}/pugixml/src
-)
+add_subdirectory(pugixml)

thirdparty/pugixml/pugixml/CMakeLists.txt

+add_library(pugixml INTERFACE)
+target_sources(pugixml INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src/pugiconfig.hpp>
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src/pugixml.hpp>
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src/pugixml.cpp>
+)
+target_include_directories(pugixml INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
+)
+install(TARGETS pugixml EXPORT adios2Exports)