#590: Only fiddle with BOOST_ROOT if it's not been set naturally

CMakeLists.txt

@@ -66,16 +66,13 @@ set(Boost_USE_STATIC_LIBS OFF)
 set(Boost_USE_MULTITHREADED ON)
 set(Boost_USE_STATIC_RUNTIME OFF)
 
-if(DEFINED ENV{BOOST_ROOT})
-    #set(Boost_INCLUDE_DIR $ENV{BOOST_ROOT})
-    set(BOOST_ROOT $ENV{BOOST_ROOT})
-else()
+if(NOT DEFINED BOOST_ROOT AND NOT DEFINED ENV{BOOST_ROOT})
     # Look for version-specific Boost directory if available (known from Github Actions VM docs)
     if(DEFINED ENV{BOOST_ROOT_1_72_0})
         set(BOOST_ROOT $ENV{BOOST_ROOT_1_72_0})
-        set(ENV{BOOST_ROOT} $ENV{BOOST_ROOT_1_72_0})
+        message(STATUS "Using value of \$ENV{BOOST_ROOT_1_72_0} to set BOOST_ROOT=$ENV{BOOST_ROOT_1_72_0}")
     else()
-        message(STATUS "No Boost root: $ENV{BOOST_ROOT}")
+        message(STATUS "No BOOST_ROOT set")
     endif()
 endif()