gcc-10 error (with RVM): mark Ruby_INCLUE_DIRS as SYSTEM

Avoid 

```
/home/julien/.conan/data/openstudio_ruby/2.7.2/nrel/testing/package/8c98c8e7c8941d8bf2c5b65aa3303761e4c9336c/include/ruby-2.7.0/ruby/backward/cxxanyargs.hpp: In function 'VALUE ruby::backward::cxxanyargs::rb_rescue(VALUE (*)(...), VALUE, VALUE (*)(...), VALUE)':
/home/julien/.conan/data/openstudio_ruby/2.7.2/nrel/testing/package/8c98c8e7c8941d8bf2c5b65aa3303761e4c9336c/include/ruby-2.7.0/ruby/backward/cxxanyargs.hpp:202:14: error: 'VALUE ruby::backward::cxxanyargs::rb_rescue(VALUE (*)(...), VALUE, VALUE (*)(...), VALUE)' is deprecated: Use of ANYARGS in this function is deprecated [-Werror=deprecated-declarations]
```

ProjectMacros.cmake

@@ -304,7 +304,7 @@ macro(MAKE_SWIG_TARGET NAME SIMPLENAME KEY_I_FILE I_FILES PARENT_TARGET PARENT_S
     set_target_properties(${swig_target} PROPERTIES LIBRARY_OUTPUT_DIRECTORY "${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/ruby/")
     set_target_properties(${swig_target} PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/ruby/")
     target_link_libraries(${swig_target} ${${PARENT_TARGET}_depends})
-    target_include_directories(${swig_target} PRIVATE ${RUBY_INCLUDE_DIRS})
+    target_include_directories(${swig_target} SYSTEM PRIVATE ${RUBY_INCLUDE_DIRS})
     add_dependencies(${swig_target} ${PARENT_TARGET})
 
     # QT-Separation-Move

ruby/CMakeLists.txt

@@ -16,7 +16,7 @@ add_library( init_openstudio OBJECT
   init_openstudio.cpp
   RubyAPI.hpp
 )
-target_include_directories(init_openstudio PRIVATE ${RUBY_INCLUDE_DIRS})
+target_include_directories(init_openstudio SYSTEM PRIVATE ${RUBY_INCLUDE_DIRS})
 
 if(MSVC)
   # TODO: JM 2019-01-04: @macumber it seems like all three targets use the same COMPILE_FLAGS,
@@ -39,7 +39,7 @@ add_library(
 )
 set_target_properties(openstudio_rb PROPERTIES PREFIX "")
 set_target_properties(openstudio_rb PROPERTIES OUTPUT_NAME openstudio)
-target_include_directories(openstudio_rb PRIVATE ${RUBY_INCLUDE_DIRS})
+target_include_directories(openstudio_rb SYSTEM PRIVATE ${RUBY_INCLUDE_DIRS})
 
 # change output directory so the openstudio.pdb file does not conflict between this target and the CLI
 set_target_properties(openstudio_rb PROPERTIES ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/ruby/")