Document that compiling a binary with Clang on Linux adds a .llvm s…

…uffix

This can result in people running old binaries unexpectedly, so it's
important to mention this suffix.

development/compiling/compiling_for_x11.rst

@@ -218,5 +218,8 @@ then use the following SCons command::
 
     scons platform=x11 use_llvm=yes use_lld=yes
 
+After the build is completed, a new binary with a ``.llvm`` suffix will be
+created in the ``bin/`` folder.
+
 It's still recommended to use GCC for production builds as they can be compiled using
 link-time optimization, making the resulting binaries smaller and faster.