FindBoost: Add support for Boost 1.73

Run `Utilities/Scripts/BoostScanDeps.cmake` with the Boost 1.73.0
sources to compute dependencies.

This includes a new Boost.Nowide library.

Special case: Boost.Filesystem is an optional dependency as the include
is only required to make Boost.Filesystem use UTF-8 paths on user
request

Modules/FindBoost.cmake

@@ -1147,7 +1147,7 @@ function(_Boost_COMPONENT_DEPENDENCIES component _ret)
       set(_Boost_TIMER_DEPENDENCIES chrono)
       set(_Boost_WAVE_DEPENDENCIES filesystem serialization thread chrono date_time atomic)
       set(_Boost_WSERIALIZATION_DEPENDENCIES serialization)
-    else()
+    elseif(Boost_VERSION_STRING VERSION_LESS 1.73.0)
       set(_Boost_CONTRACT_DEPENDENCIES thread chrono date_time)
       set(_Boost_COROUTINE_DEPENDENCIES context)
       set(_Boost_FIBER_DEPENDENCIES context)
@@ -1161,6 +1161,20 @@ function(_Boost_COMPONENT_DEPENDENCIES component _ret)
       set(_Boost_TIMER_DEPENDENCIES chrono)
       set(_Boost_WAVE_DEPENDENCIES filesystem serialization thread chrono date_time atomic)
       set(_Boost_WSERIALIZATION_DEPENDENCIES serialization)
+    else()
+      set(_Boost_CONTRACT_DEPENDENCIES thread chrono date_time)
+      set(_Boost_COROUTINE_DEPENDENCIES context)
+      set(_Boost_FIBER_DEPENDENCIES context)
+      set(_Boost_IOSTREAMS_DEPENDENCIES regex)
+      set(_Boost_LOG_DEPENDENCIES date_time log_setup filesystem thread regex chrono atomic)
+      set(_Boost_MATH_DEPENDENCIES math_c99 math_c99f math_c99l math_tr1 math_tr1f math_tr1l atomic)
+      set(_Boost_MPI_DEPENDENCIES serialization)
+      set(_Boost_MPI_PYTHON_DEPENDENCIES python${component_python_version} mpi serialization)
+      set(_Boost_NUMPY_DEPENDENCIES python${component_python_version})
+      set(_Boost_THREAD_DEPENDENCIES chrono date_time atomic)
+      set(_Boost_TIMER_DEPENDENCIES chrono)
+      set(_Boost_WAVE_DEPENDENCIES filesystem serialization thread chrono date_time atomic)
+      set(_Boost_WSERIALIZATION_DEPENDENCIES serialization)
       if(NOT Boost_VERSION_STRING VERSION_LESS 1.73.0)
         message(WARNING "New Boost version may have incorrect or missing dependencies and imported targets")
       endif()
@@ -1226,6 +1240,7 @@ function(_Boost_COMPONENT_HEADERS component _hdrs)
   set(_Boost_MPI_HEADERS                 "boost/mpi.hpp")
   set(_Boost_MPI_PYTHON_HEADERS          "boost/mpi/python/config.hpp")
   set(_Boost_NUMPY_HEADERS               "boost/python/numpy.hpp")
+  set(_Boost_NOWIDE_HEADERS              "boost/nowide/cstdlib.hpp")
   set(_Boost_PRG_EXEC_MONITOR_HEADERS    "boost/test/prg_exec_monitor.hpp")
   set(_Boost_PROGRAM_OPTIONS_HEADERS     "boost/program_options.hpp")
   set(_Boost_PYTHON_HEADERS              "boost/python.hpp")

Utilities/Scripts/BoostScanDeps.cmake

@@ -139,6 +139,12 @@ function(_Boost_FIND_COMPONENT_DEPENDENCIES component includedir _ret_libs)
             # hard dependency (handle as special-case for numpy).
             continue()
           endif()
+          if(component STREQUAL "nowide" AND
+             _boost_component_match STREQUAL "filesystem")
+            # Optional filesystem dependency; skip to avoid making it a
+            # hard dependency.
+            continue()
+          endif()
           if (_boost_dep_found EQUAL -1 AND
               NOT "${_boost_component_match}" STREQUAL "${component}")
             list(APPEND _boost_DEPS "${_boost_component_match}")