config: allow --with-pmi=path/to/libpmi

Allow linking with an externally installed libpmi.so. We'll assume using
PMIv1, but eventually we may allow runtime selections.

confdb/aclocal_libs.m4

@@ -18,7 +18,9 @@ dnl TODO as written, this macro cannot handle a "with_option" arg that has "-"
 dnl characters in it.  Use AS_TR_SH (and possibly AS_VAR_* macros) to handle
 dnl this case if it ever arises.
 AC_DEFUN([PAC_SET_HEADER_LIB_PATH],[
-    AC_ARG_WITH([$1], [AS_HELP_STRING([--with-$1=[[PATH]]],PAC_WITH_LIB_HELP_STRING($1))])
+    m4_ifdef([skip_ac_arg_with_$1], [], [
+        AC_ARG_WITH([$1], [AS_HELP_STRING([--with-$1=[[PATH]]],PAC_WITH_LIB_HELP_STRING($1))])
+    ])
 
     AC_ARG_WITH([$1-include],
                 [AS_HELP_STRING([--with-$1-include=PATH],

configure.ac

@@ -1501,6 +1501,16 @@ case "$with_pmi" in
     with_pmi=pmi2
     with_pmilib=mpich
     ;;
+  pmi1|pmi2)
+    ;;
+  *)
+    # allow user to specify an external libpmi
+    m4_define([skip_ac_arg_with_pmi], 1)
+    PAC_CHECK_HEADER_LIB_FATAL([pmi], [pmi.h], [pmi], [PMI_Init])
+    # assume using PMI-1
+    with_pmi=pmi1
+    with_pmilib=no
+    ;;
 esac
 
 case "$with_pmilib" in
@@ -1690,6 +1700,9 @@ case "$with_pmilib" in
   pmix)
     # taken care of by PAC_CHECK_HEADER_LIB_EXPLICIT
     ;;
+  no)
+    # taken care of by --with-pmi=path
+    ;;
   *)
     AC_MSG_ERROR([pmilib $with_pmilib not supported.])
     ;;