sim: cris: use -sim with C tests for cris-elf targets

Building the C tests with a cris-elf toolchain (gcc-10.2 &
newlib-4.1.0) currently fail due to warnings it emits:
cris-elf-ld: libc.a(lib_a-closer.o): in function `_close_r':
newlib/libc/reent/closer.c:47: warning: _close is not implemented and will always fail

This is because the default target for cris-elf is bare metal, not
the simulator.  For that, we need -sim.  So add it for elf targets.

We don't add it for all targets as the simulator (and testsuite)
run both libgloss programs as well as Linux userspace programs.

sim/testsuite/sim/cris/ChangeLog

@@ -1,3 +1,7 @@
+2021-01-07  Mike Frysinger  <vapier@gentoo.org>
+
+	* c/c.exp [cris*-*-elf] (CFLAGS_FOR_TARGET): Add -sim.
+
 2021-01-07  Mike Frysinger  <vapier@gentoo.org>
 
 	* c/kill2.c: Include unistd.h.

sim/testsuite/sim/cris/c/c.exp

@@ -26,6 +26,10 @@ if [istarget cris-*-*] {
     set mach "crisv32"
 }
 
+if [istarget cris*-*-elf] {
+    append CFLAGS_FOR_TARGET " -sim"
+}
+
 # Using target_compile, since it is less noisy,
 if { [target_compile $srcdir/$subdir/hello.c compilercheck.x \
 	  "executable" "" ] == "" } {