Show a message explaining how to build LLVM when a pre-built package is unavailable.

build/scripts/LLVM.lua

@@ -186,9 +186,22 @@ function download_llvm()
 
   -- check if we already have the file downloaded
   if os.isfile(archive) then
-  	  print("Archive " .. archive .. " already exists.")
-  else
-	  download(base .. archive, archive)
+    print("Archive " .. archive .. " already exists.")
+  else  
+    msg, code = download(base .. archive, archive, true)
+    
+    if msg ~= "OK" then
+    	if code == 404 then
+        print("Error: " .. archive .. " is unavailable.")
+        print("Please create your own LLVM package by executing the following commands:")
+        print("./build.sh clone_llvm")
+        print("./build.sh build_llvm")
+        print("./build.sh package_llvm")
+        os.exit(1)
+      end
+      
+      error(msg)
+    end
   end
 
   -- extract the package

build/scripts/Utils.lua

@@ -93,19 +93,23 @@ function http.progress (total, prev, curr)
   end
 end
 
-function download(url, file)
+function download(url, file, try)
   print("Downloading: " .. url)
   local prev = 0
-  local res = http.download(url, file, function(total, curr)
+  local res, code = http.download(url, file, function(total, curr)
     http.progress(total, prev, curr)
     prev = curr
   end)
 
   if res ~= "OK" then
     os.remove(file)
-    error(res)
+
+    if not try then
+      error(res)
+    end
   end
-  return res
+  
+  return res, code
 end
 
 --