test: move trim to global helpers

test/unit/helpers.lua

@@ -16,6 +16,7 @@ local neq = global_helpers.neq
 local map = global_helpers.map
 local eq = global_helpers.eq
 local ok = global_helpers.ok
+local trim = global_helpers.trim
 
 -- C constants.
 local NULL = ffi.cast('void*', 0)
@@ -120,10 +121,6 @@ local deinit = only_separate(function()
   end
 end)
 
-local function trim(s)
-  return s:match('^%s*(.*%S)') or ''
-end
-
 -- a Set that keeps around the lines we've already seen
 local cdefs_init = Set:new()
 local cdefs_mod = nil