> Then, it probably does not react to neither of below options:
>         -showme:compile
>         -showme:link
>         -showme
>         -show
> What option to mpCC is supposed to print additional compiler flags to use?

You are correct in that none of the showme or show options seem to give any additional information.

Typically for xlC(vacpp) the -v option is used report progress of the compilation and report the names of the programs being invoked as well as the options being specified to each program.  I tried it with mpCC and it dumps the following:
bash-3.00$ mpCC -v

xlC_r -I/usr/lpp/ppe.poe/include -binitfini:poe_remote_main -lmpi_r -lvtd_r -v -lpthreads -L/usr/lpp/ppe.poe/lib/threads -L/usr/lpp/ppe.poe/lib -L/usr/lpp/ppe.poe/lib/ip

as well as some other information that is likely not relevant.  The above line is the first list displayed but several others follow.

Chris Cambly
XL C++ Compiler Development