update from upstream, add extra target for extra headerfiles

CMakeLists.txt

@@ -67,15 +67,20 @@ target_include_directories( date INTERFACE
 # adding header sources just helps IDEs
 target_sources( date INTERFACE
     $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/date.h
-    # the rest of these are not currently part of the public interface of the library:
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/solar_hijri.h>
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/islamic.h>
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/iso_week.h>
-    $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include/date/julian.h>
 )
+
+add_library(extra INTERFACE)
+add_library(date::extra ALIAS extra)
+target_sources(extra INTERFACE
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/solar_hijri.h
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/islamic.h
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/include>$<INSTALL_INTERFACE:include>/date/julian.h
+)
+
 if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.15)
     # public headers will get installed:
-    set_target_properties( date PROPERTIES PUBLIC_HEADER include/date/date.h )
+    set_target_properties( date PROPERTIES PUBLIC_HEADER include/date/date.h)
+    set_target_properties( extra PROPERTIES PUBLIC_HEADER "include/date/islamic.h;include/date/solar_hijri.h;include/date/julian.h")
 endif ()
 
 # These used to be set with generator expressions,
@@ -166,10 +171,10 @@ if( BUILD_TZ_LIB )
         PUBLIC_HEADER "${TZ_HEADERS}"
         VERSION "${PROJECT_VERSION}"
         SOVERSION "${ABI_VERSION}" )
-    if( NOT MSVC )
-        find_package( Threads )
-        target_link_libraries( date-tz PUBLIC Threads::Threads )
-    endif( )
+
+    find_package( Threads )
+    target_link_libraries( date-tz PUBLIC Threads::Threads )
+
     if( NOT USE_SYSTEM_TZ_DB AND NOT MANUAL_TZ_DB )
         find_package( CURL REQUIRED )
         target_include_directories( date-tz SYSTEM PRIVATE ${CURL_INCLUDE_DIRS} )
@@ -192,6 +197,11 @@ install( TARGETS date
     PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date )
 export( TARGETS date NAMESPACE date:: FILE dateTargets.cmake )
 
+install( TARGETS extra
+        EXPORT dateTargets
+        PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date)
+export(TARGETS extra NAMESPACE date:: APPEND FILE dateTargets.cmake)
+
 install( TARGETS iso_week
         EXPORT dateTargets
         PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/date )
@@ -225,9 +235,6 @@ install( EXPORT dateTargets
   FILE dateTargets.cmake
   NAMESPACE date::
   DESTINATION ${CONFIG_LOC} )
-install (
-  FILES cmake/dateConfig.cmake "${version_config}"
-  DESTINATION ${CONFIG_LOC})
 
 configure_file(cmake/dateConfig.cmake.in dateConfig.cmake @ONLY)
 install(FILES "${CMAKE_CURRENT_BINARY_DIR}/dateConfig.cmake"