Make the $MAKE env variable be precious in configure, per

recomendation from Paul Hargrove, and add a blurb about it in README
to explain why that's important.

This commit was SVN r25925.

README

@@ -1064,6 +1064,18 @@ shell$ ./configure CC=mycc CXX=myc++ F77=myf77 F90=myf90 ...
    variables and values in the config.log file, which makes
    post-mortem analysis easier when problems occur.
 
+Note that if you intend to compile Open MPI with a "make" other than
+the default one in your PATH, then you must either set the $MAKE
+environment variable before invoking Open MPI's configure script, or
+pass "MAKE=your_make_prog" to configure.  For example:
+
+shell$ ./configure MAKE=/path/to/my/make ...
+
+This could be the case, for instance, if you have a shell alias for
+"make", or you always type "gmake" out of habit.  Failure to tell
+configure which non-default "make" you will use to compile Open MPI
+can result in undefined behavior (meaning: don't do that).
+
 Note that you may also want to ensure that the value of
 LD_LIBRARY_PATH is set appropriately (or not at all) for your build
 (or whatever environment variable is relevant for your operating

configure.ac

@@ -92,6 +92,10 @@ AM_INIT_AUTOMAKE([foreign dist-bzip2 subdir-objects no-define 1.11 tar-ustar])
 # (even though they're supposed to be identical).  Shrug.
 AM_SILENT_RULES([yes])
 
+# Per some discussion on the list, regard the "MAKE" variable as
+# precious.
+AC_ARG_VAR([MAKE], [The "make" command])
+
 # Make configure depend on the VERSION file, since it's used in AC_INIT
 AC_SUBST([CONFIGURE_DEPENDENCIES], ['$(top_srcdir)/VERSION'])