[Bug fortran/67068] Ambiguous interfaces generated when including open mip fortran header

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67068

--- Comment #6 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
For openmpi-1.10.0 and trunk (6.0) compiling examples/hello_mpifh.f with
-freal-4-real-8 gives

mpif-sizeof.h:575:72:


Error: Ambiguous interfaces 'mpi_sizeof_real64_r7' and 'mpi_sizeof_real32_r7'
in generic interface 'mpi_sizeof' at (1)
mpif-sizeof.h:1139:72:


Error: Ambiguous interfaces 'pmpi_sizeof_real64_r7' and 'pmpi_sizeof_real32_r7'
in generic interface 'pmpi_sizeof' at (1)

If I compile with -fdefault-real-8 with/without -fdefault-double-8, I don't get
the error.

The (a) main difference between -fdefault-double-8 and -freal-4-real-8 is that
the former converts only default REAL (not the variables defined as REAL(4)),
while the later converts all REAL to REAL(8).

Anyway mixing -fdefault-double-8 and -freal-4-real-8 is bad (as in forbidden).

IMO this PR should be closed as INVALID.