tests: add a specification test

Author: zerbina

tests/lang/s02_core/s02_procedures/t99_underscore_parameter.nim

@@ -0,0 +1,19 @@
+discard """
+  description: '''
+    Multiple parameters can use an underscore as the name, making the
+    parameters inaccessible
+  '''
+"""
+
+proc test1(_: int) = discard
+test1(1)
+
+proc test2(_: int, _: int) = discard
+test2(1, 2)
+
+proc mixed(a: int, _: int) = discard
+mixed(1, 2)
+
+## The same is true for parameters of anonymous procedures.
+let anon = proc(_, _, _: int) = discard
+anon(1, 2, 3)