net/mpich: work-around to build the dependencies on -CURRENT

Since the switch from clang-16 to 17.0.6 on -CURRENT, MPICH encounters
linker errors.

A work-around to force the usage of clang <= 16 has been introduced in
eb36006fdb70, but when the compiler has been forced to build, it must be
kept to build the dependencies.

PR: 276035