Remove C compiler replacement in MPI case.

* There is no simple way to guess an MPI enabled compiler-setup.

configure

@@ -25977,15 +25977,6 @@ else
   enable_mpi=no
 fi
-if test "${enable_mpi}" = "yes"; then :
-  if test "${host_os%???}" = "aix"; then :
-  replace_cc="mpicc"
-else
-  replace_cc="mpcc_r"
-fi
-else
-  replace_cc=$CC
-fi
 #  ----------------------------------------------------------------------
 #  Create the Fortran Interface via iso_c_binding module (Fortran 2003 Standard)
 # Check whether --enable-iso-c-interface was given.
@@ -26441,10 +26432,6 @@ fi
-if test "x${replace_cc}" != "x"; then :
-  CC=$replace_cc
-fi
-
 ac_config_files="$ac_config_files Makefile src/Makefile interfaces/Makefile app/Makefile tests/Makefile examples/Makefile cdi.settings src/pkgconfig/cdi.pc"
 cat >confcache <<\_ACEOF

configure.ac

@@ -87,11 +87,6 @@ ACX_OPTIONS
 #  ----------------------------------------------------------------------
 # Compile with MPI support
 AC_ARG_ENABLE(mpi,AS_HELP_STRING([--enable-mpi],[Compile with MPI compiler [default=no]]),enable_mpi=${enableval},enable_mpi=no)
-AS_IF([test "${enable_mpi}" = "yes"],
-      [AS_IF([test "${host_os%???}" = "aix"],
-             [replace_cc="mpicc"],
-             [replace_cc="mpcc_r"])],
-      [replace_cc=$CC])
 #  ----------------------------------------------------------------------
 #  Create the Fortran Interface via iso_c_binding module (Fortran 2003 Standard)
 AC_ARG_ENABLE(iso-c-interface,
@@ -170,8 +165,6 @@ ACX_CHECK_CFINT([$srcdir/src/cfortran.h])
 
 AC_SUBST([CPPFLAGS])
 
-AS_IF([test "x${replace_cc}" != "x"],[CC=$replace_cc])
-
 AC_OUTPUT([Makefile src/Makefile interfaces/Makefile app/Makefile \
    tests/Makefile examples/Makefile cdi.settings src/pkgconfig/cdi.pc])