FindBoost: Fixes #12188

Workaround an issue where users wanted to use Boost_LIBRARIES with the
install() command and debug/optimized keywords were interfering.  Now
debug/optimized keywords are removed if the release & debug library
are the same.

Modules/FindBoost.cmake

@@ -281,6 +281,12 @@ macro(_Boost_ADJUST_LIB_VARS basename)
       set(Boost_${basename}_LIBRARY         ${Boost_${basename}_LIBRARY_DEBUG})
       set(Boost_${basename}_LIBRARIES       ${Boost_${basename}_LIBRARY_DEBUG})
     endif()
+
+    # If the debug & release library ends up being the same, omit the keywords
+    if(${Boost_${basename}_LIBRARY_RELEASE} STREQUAL ${Boost_${basename}_LIBRARY_DEBUG})
+      set(Boost_${basename}_LIBRARY   ${Boost_${basename}_LIBRARY_RELEASE} )
+      set(Boost_${basename}_LIBRARIES ${Boost_${basename}_LIBRARY_RELEASE} )
+    endif()
     
     if(Boost_${basename}_LIBRARY)
       set(Boost_${basename}_LIBRARY ${Boost_${basename}_LIBRARY} CACHE FILEPATH "The Boost ${basename} library")