fix #17286 nim check -b:js works (#19704)

* fix #17286 nim check -b:js works

* fix

tests/misc/t17286.nim

@@ -0,0 +1,16 @@
+discard """
+  cmd: "nim check -b:js $file"
+  action: "compile"
+"""
+
+# bug #17286
+
+import std/compilesettings
+
+static:
+  doAssert querySetting(backend) == "js"
+  doAssert defined(js)
+  doAssert not defined(c)
+
+import random
+randomize()