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.
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