torture: Cause mkinitrd.sh to indicate failure on compile errors

Currently, if the C program created by mkinitrd.sh has compile errors,
the errors are printed, but kvm.sh soldiers on, building kernels that
have init-less initrd setups.  The kernels then fail on boot when they
attempt to mount non-existent root filesystems.

This commit therefore improves user friendliness by making mkinitrd.sh
return non-zero exit status on compile errors, which in turn causes kvm.sh
to take an early exit, with the compile errors still clearly visible.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/rcutorture/bin/mkinitrd.sh

@@ -74,8 +74,16 @@ if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
         ${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
 		-nostdlib -include ../../../../include/nolibc/nolibc.h \
 		-s -static -Os -o init init.c -lgcc
+	ret=$?
 else
 	${CROSS_COMPILE}gcc -s -static -Os -o init init.c
+	ret=$?
+fi
+
+if [ "$ret" -ne 0 ]
+then
+	echo "Failed to create a statically linked C-language initrd"
+	exit "$ret"
 fi
 
 rm init.c