Build order with gprbuild

[Gautier write-only address <gautier_niouzes@hotmail.com>]

When a GNAT project A depends on project B, is there a simple (*) way to make gprbuild build project B before starting the build of A?
It would be useful when project B generates Ada sources…
Example:

with "code_generation.gpr";

project Main is
  for Source_Dirs use (".", "gen");
  for Object_Dir use "obj";
  for Create_Missing_Dirs use "True";  --  Flips by default the "-p" switch
  for Main use ("main.adb");
end Main;

(*) By “simple” I mean simpler than the way described here:
https://www.adacore.com/gems/gem-157-gprbuild-and-code-generation