Added _latomic build word postfix for building on the pi4. Also added postfixes to readme.md.

README.md

@@ -132,6 +132,32 @@ Note: to easily run the editor you can use the `editor.sh` or `editor.bat` in th
 
 Append `v` to pass the `vsproj=yes` parameter to the build script. This will generate Visual Studio project files.
 
+
+#### Postfixes
+
+There are a few postfixes for the build words. These are more complex options. You have to append them to your build word with an underscore.
+
+You can use as many as you want.
+
+For example:
+
+``` scons bel_slim_latomic -j4 ```
+
+##### slim
+
+With this postfix you can build a slimmed down version of the engine. This disables quite a few unneeded modules.
+
+``` scons bel_slim -j4 ```
+
+##### latomic
+
+If you get linker errors while building the game/editor about undefined referenced with atomic related functions you can use this postfix.
+It will add the ` -latomic ` command line switch to the linker flags.
+
+I ran into this issue while building on a raspberry pi 4 with the x11 platform. It might be related to the recent reworks to threading.
+
+``` scons bel_latomic -j4 ```
+
 #### Scons cache, and sdk locations
 
 In order to use scons cache and to tell the build system where some of the required sdks are located you usually 

SConstruct

@@ -350,6 +350,10 @@ if len(sys.argv) > 1:
             build_string += 'module_webm_enabled=no module_webp_enabled=no module_arkit_enabled=no module_visual_script_enabled=no module_gdnative_enabled=no module_mobile_vr_enabled=no module_theora_enabled=no module_xatlas_unwrap_enabled=no no_editor_splash=yes module_bullet_enabled=no module_camera_enabled=no module_csg_enabled=no module_denoise_enabled=no module_fbx_enabled=no module_gridmap_enabled=no module_hdr_enabled=no module_lightmapper_cpu_enabled=no module_raycast_enabled=no module_recast_enabled=no module_vhacd_enabled=no module_webxr_enabled=no'
             build_string += ' '
 
+        if 'latomic' in arg_split:
+            build_string += 'LINKFLAGS="-latomic"'
+            build_string += ' '
+
         target = ' '
 
         if 'E' in arg: