Fix os.outputof for lua 5.3.4

src/base/os.lua

@@ -61,7 +61,7 @@
 		end
 		return dirs
 	end
-	
+
 	local function get_library_search_path()
 		local path
 		if os.istarget("windows") then
@@ -151,14 +151,14 @@
 	function os.findheader(headerpath, headerdirs)
 		-- headerpath: a partial header file path
 		-- headerdirs: additional header search paths
-		
+
 		local path = get_library_search_path()
-		
+
 		-- replace all /lib by /include
 		path = path .. ':'
-		path = path:gsub ('/lib[0-9]*([:/])', '/include%1') 
+		path = path:gsub ('/lib[0-9]*([:/])', '/include%1')
 		path = path:sub (1, #path - 1)
-		
+
 		local userpath = ""
 
 		if type(headerdirs) == "string" then
@@ -174,7 +174,7 @@
 				path = userpath
 			end
 		end
-		
+
 		local result = os.pathsearch (headerpath, path)
 		return result
 	end
@@ -460,17 +460,17 @@
 
 		local pipe = io.popen(cmd .. " 2>&1")
 		local result = pipe:read('*a')
-		local b, exitcode = pipe:close()
-		if not b then
-			exitcode = -1
-		end
+		local success, what, code = pipe:close()
+		if success then
+			-- chomp trailing newlines
+			if result then
+				result = string.gsub(result, "[\r\n]+$", "")
+			end
 
-		-- chomp trailing newlines
-		if result then
-			result = string.gsub(result, "[\r\n]+$", "")
+			return result, code, what
+		else
+			return nil, code, what
 		end
-
-		return result, exitcode
 	end