[MC,ELF] .section: unconditionally print section flag 'G' after 'o'

* Placing 'G' before 'M' (SHF_MERGE) can be misleading as the sh_entsize
  argument goes before the section group name, if a reader doesn't know
  that the order of extra arguments is not affected by the order of flags.
* 'a', 'w', and 'x' indicate basic permission-related flags. Separating
  them with 'G' is kinda ugly.

Simplify code and move 'G' after 'o'. The new output is more similar to
GCC.