add missing json files

external/json/cmake/config.cmake.in

@@ -0,0 +1,15 @@
+include(FindPackageHandleStandardArgs)
+set(${CMAKE_FIND_PACKAGE_NAME}_CONFIG ${CMAKE_CURRENT_LIST_FILE})
+find_package_handle_standard_args(@PROJECT_NAME@ CONFIG_MODE)
+
+if(NOT TARGET @PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@)
+    include("${CMAKE_CURRENT_LIST_DIR}/@NLOHMANN_JSON_TARGETS_EXPORT_NAME@.cmake")
+    if((NOT TARGET @NLOHMANN_JSON_TARGET_NAME@) AND
+       (NOT @PROJECT_NAME@_FIND_VERSION OR
+        @PROJECT_NAME@_FIND_VERSION VERSION_LESS 3.2.0))
+        add_library(@NLOHMANN_JSON_TARGET_NAME@ INTERFACE IMPORTED)
+        set_target_properties(@NLOHMANN_JSON_TARGET_NAME@ PROPERTIES
+            INTERFACE_LINK_LIBRARIES @PROJECT_NAME@::@NLOHMANN_JSON_TARGET_NAME@
+        )
+    endif()
+endif()

external/json/cmake/nlohmann_jsonConfigVersion.cmake.in

@@ -0,0 +1,20 @@
+# This is essentially cmake's BasicConfigVersion-SameMajorVersion.cmake.in but
+# without the 32/64-bit check.  Since json is a header-only library, it doesn't
+# matter if it was built on a different platform than what it is used on (see
+# https://github.com/nlohmann/json/issues/1697).
+set(PACKAGE_VERSION "@PROJECT_VERSION@")
+
+if(PACKAGE_VERSION VERSION_LESS PACKAGE_FIND_VERSION)
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+else()
+
+  if(PACKAGE_FIND_VERSION_MAJOR STREQUAL "@PROJECT_VERSION_MAJOR@")
+    set(PACKAGE_VERSION_COMPATIBLE TRUE)
+  else()
+    set(PACKAGE_VERSION_COMPATIBLE FALSE)
+  endif()
+
+  if(PACKAGE_FIND_VERSION STREQUAL PACKAGE_VERSION)
+      set(PACKAGE_VERSION_EXACT TRUE)
+  endif()
+endif()

external/json/cmake/pkg-config.pc.in

@@ -0,0 +1,7 @@
+prefix=@CMAKE_INSTALL_PREFIX@
+includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+
+Name: @PROJECT_NAME@
+Description: JSON for Modern C++
+Version: @PROJECT_VERSION@
+Cflags: -I${includedir}