AX_MPI: Fix recommendation for compiling everything with MPI.

Fix typos when compiling everything with MPI. Update description to
include defaulting CC to MPICC if only the latter was set. See

  http://lists.gnu.org/archive/html/autoconf-archive-maintainers/2010-08/msg00000.html

for further details.

1 files changed, 13 insertions, 4 deletions

diff --git a/m4/ax_mpi.m4 b/m4/ax_mpi.m4
index 06c0abd..d2dff18 100644
--- a/m4/ax_mpi.m4
+++ b/m4/ax_mpi.m4
@@ -19,10 +19,19 @@
 #   are needed for linking MPI (e.g. -lmpi or -lfmpi, if a special
 #   MPICC/MPICXX/MPIF77/MPIFC was not found).
 #
-#   If you want to compile everything with MPI, you should set:
+#   If you want to compile everything with MPI, you should use something like
+#   this for C:
 #
-#     CC="MPICC" #OR# CXX="MPICXX" #OR# F77="MPIF77" #OR# FC="MPIFC"
-#     LIBS="$MPILIBS $LIBS"
+#       if test -z "$CC" && test -n "$MPICC"; then
+#         CC="$MPICC"
+#       fi
+#       AC_PROG_CC
+#       AX_MPI
+#       CC="$MPICC"
+#       LIBS="$MPILIBS $LIBS"
+#
+#   and similar for C++ (change all instances of CC to CXX), Fortran 77
+#   (with F77 instead of CC) or Fortran (with FC instead of CC).
 #
 #   NOTE: The above assumes that you will use $CC (or whatever) for linking
 #   as well as for compiling. (This is the default for automake and most
@@ -67,7 +76,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 5
+#serial 6
 
 AU_ALIAS([ACX_MPI], [AX_MPI])
 AC_DEFUN([AX_MPI], [