[legacy] boost: Fix python and icu config

FairSoftConfig.cmake

@@ -62,3 +62,16 @@ if(APPLE)
   set(PYTHON_EXECUTABLE "${python_prefix}/bin/python3" CACHE FILEPATH "Python executable" FORCE)
 endif()
 # set(PYTHON_EXECUTABLE "/some/other/path/to/python" CACHE FILEPATH "Python executable" FORCE)
+
+#
+# ICU
+#
+#  On macOS we assume you have used <source-dir>/legacy/setup-macos.sh which
+#  installs ICU via Homebrew. That the Homebrew-based ICU is chosen over the
+#  native macOS ICU we have to hint its location:
+#
+if(APPLE)
+  execute_process(COMMAND brew --prefix icu4c OUTPUT_VARIABLE icu_prefix)
+  string(STRIP "${icu_prefix}" icu_prefix)
+  set(ICU_ROOT "${icu_prefix}" CACHE FILEPATH "ICU prefix" FORCE)
+endif()

cmake/legacy.cmake

@@ -47,8 +47,14 @@ if(APPLE)
   )
 endif()
 unset(python)
+if(ICU_ROOT)
+  set(icu "-DICU_ROOT=${ICU_ROOT}")
+  set(boost_icu_config "--with-icu=${ICU_ROOT}")
+endif()
 if(PYTHON_EXECUTABLE)
   set(python "-DPYTHON_EXECUTABLE=${PYTHON_EXECUTABLE}")
+  get_filename_component(PYTHON_EXECUTABLE_FILE "${PYTHON_EXECUTABLE}" NAME)
+  set(boost_python_config "--with-python=${PYTHON_EXECUTABLE_FILE}")
 endif()
 set(LOG_TO_FILE
   LOG_DIR "${CMAKE_BINARY_DIR}/Log"
@@ -95,6 +101,7 @@ ExternalProject_Add(boost
   BUILD_IN_SOURCE ON
   CONFIGURE_COMMAND "./bootstrap.sh"
     "--prefix=${CMAKE_INSTALL_PREFIX}"
+    ${boost_python_config} ${boost_icu_config}
   PATCH_COMMAND ${patch} -p2 -i "${CMAKE_SOURCE_DIR}/legacy/boost/1.72_boost_process.patch"
   BUILD_COMMAND "./b2" "--layout=system"
     "cxxstd=${CMAKE_CXX_STANDARD}"