Add CLI tests for RGBASM

test/asm/cli/multiple-inputs.err

@@ -0,0 +1,17 @@
+FATAL: More than one input file specified
+Usage: rgbasm [-EhVvw] [-B depth] [-b chars] [-D name[=value]] [-g chars]
+              [-I path] [-M depend_file] [-MC] [-MG] [-MP] [-MT target_file]
+              [-MQ target_file] [-o out_file] [-P include_file] [-p pad_value]
+              [-Q precision] [-r depth] [-s features:state_file] [-W warning]
+              [-X max_errors] <file>
+
+Useful options:
+    -E, --export-all               export all labels
+    -M, --dependfile <path>        set the output dependency file
+    -o, --output <path>            set the output object file
+    -p, --pad-value <value>        set the value to use for `DS`
+    -s, --state <features>:<path>  set an output state file
+    -V, --version                  print RGBASM version and exit
+    -W, --warning <warning>        enable or disable warnings
+
+For more help, use "man rgbasm" or go to https://rgbds.gbdev.io/docs/