Fix order of evaluation issue when compiling regex alternations

The previous implementation was relying on the left hand side of the
assignement's side effects to be sequenced before the right hand side
evaluation (so --split_pos was expected to have taken place)

This is actually counter to C++17 which guarantees evaluation of the
right hand side of the assignement first. For some reason this is
not the case with GCC on linux.

rc/tools/grep.kak

@@ -28,7 +28,7 @@ define-command -params .. -docstring %{
                 esac
             fi
             $kak_opt_grepcmd "$@" 2>&1 | tr -d '\r'
-        } %arg{@}
+        } -- %arg{@}
         set-option buffer filetype grep
         set-option buffer jump_current_line 0
     }

rc/tools/make.kak

@@ -16,7 +16,7 @@ define-command -params .. -docstring %{
         fifo -scroll -name *make* -script %{
             trap - INT QUIT
             $kak_opt_makecmd "$@"
-        } %arg{@} # pass arguments for "$@" above, exit to avoid evaluating them
+        } -- %arg{@}
         set-option buffer filetype make
         set-option buffer jump_current_line 0
     }

src/regex_impl.cc

@@ -753,7 +753,10 @@ private:
                 {
                     auto node = compile_node<direction>(child);
                     if (child != index+1)
-                        m_program.instructions[--split_pos].param.split = CompiledRegex::Param::Split{.offset = offset(node, split_pos), .prioritize_parent = true};
+                    {
+                        --split_pos;
+                        m_program.instructions[split_pos].param.split = {.offset = offset(node, split_pos), .prioritize_parent = true};
+                    }
                     if (get_node(child).children_end != end)
                     {
                         auto jump = push_inst(CompiledRegex::Jump);