Disable automatic dependency generation for the Cray compiler

Cray only supports `-M` for generating dependency files. It does not support
`-MM` or `-MT`, so don't try to use them. I just reused the existing mechanism
for turning auto-dependency generation off (`CC_MM=`), but it might be more
principled to add a configure test to check if the compiler supports `-MM` and
`-MT`, instead of manually tracking which compilers don't support those flags.

configure.ac

@@ -323,6 +323,10 @@ if test "x$je_cv_cray_prgenv_wrapper" = "xyes" ; then
   TEST_LD_MODE='-dynamic'
 fi
 
+if test "x${je_cv_cray}" = "xyes" ; then
+  CC_MM=
+fi
+
 AN_MAKEVAR([AR], [AC_PROG_AR])
 AN_PROGRAM([ar], [AC_PROG_AR])
 AC_DEFUN([AC_PROG_AR], [AC_CHECK_TOOL(AR, ar, :)])