Reduce the default verbosity of JS library error messages (emscripten-core#8339)

Currently the entire library is printed which makes seeing the
actual error very difficult.  Normally the filename and line number
should be sufficient and we can put the rest of it befind VERBOSE=1.

Author: sbc100

src/modules.js

@@ -160,11 +160,24 @@ var LibraryManager = {
         processed = processMacros(preprocess(src, filename));
         eval(processed);
       } catch(e) {
-        var details = [e, e.lineNumber ? 'line number: ' + e.lineNumber : '', (e.stack || "").toString().replace('Object.<anonymous>', filename)];
+        var details = [e, e.lineNumber ? 'line number: ' + e.lineNumber : ''];
+        if (VERBOSE) {
+          details.push((e.stack || "").toString().replace('Object.<anonymous>', filename));
+        }
         if (processed) {
-          error('failure to execute js library "' + filename + '": ' + details + '\npreprocessed source (you can run a js engine on this to get a clearer error message sometimes):\n=============\n' + processed + '\n=============\n');
+          error('failure to execute js library "' + filename + '": ' + details);
+          if (VERBOSE) {
+            error('preprocessed source (you can run a js engine on this to get a clearer error message sometimes):\n=============\n' + processed + '\n=============');
+          } else {
+            error('use -s VERBOSE to see more details')
+          }
         } else {
-          error('failure to process js library "' + filename + '": ' + details + '\noriginal source:\n=============\n' + src + '\n=============\n');
+          error('failure to process js library "' + filename + '": ' + details);
+          if (VERBOSE) {
+            error('original source:\n=============\n' + src + '\n=============');
+          } else {
+            error('use -s VERBOSE to see more details')
+          }
         }
         throw e;
       }