make the 'canimport' template work

tests/modules/tcanimport.nim

@@ -0,0 +1,19 @@
+discard """
+  output: '''ABC
+nope'''
+"""
+
+template canImport(x): bool =
+  compiles:
+    import x
+
+when canImport(strutils):
+  import strutils
+  echo "abc".toUpperAscii
+else:
+  echo "meh"
+
+when canImport(none):
+  echo "what"
+else:
+  echo "nope"