ffiimp.js: Fix compatibility with older node.js version

They seem to expect main() to be included in the dynamic libraries. Odd.

For testing on a Mac, I now encounter issues discussed at:
https://github.com/node-ffi/node-ffi/pull/363/files

src/ffiimp.js

@@ -47,17 +47,16 @@ var loadCModule = function (path, args, mraa) {
     if (path.indexOf('.c') != -1)
         path = path.replace('.c', '');
     mraa = mraa || false; // link mraa 
-    var outPath = path + '.so';
     var inPath = path + '.c';
-    var shellCmd = 'gcc -shared -fpic ' + inPath + ' -o ' + outPath;
+    var shellCmd = 'gcc -shared -fpic ' + inPath + ' -o ' + path + '.so';
     if (mraa) shellCmd += ' -lmraa';
     if (debug) winston.debug('loadCModule: shellCmd = ' + shellCmd);
 
     // Consider not running if .so newer than .c
     shell.exec(shellCmd);
 
     if (ffi.exists)
-        return ffi.Library(outPath, args);
+        return ffi.Library(path, args);
     else {
         winston.info("loadCModule: Could not load module FFI");
         return "ffi not loaded";

test/test-ffi.js

@@ -14,6 +14,12 @@ int dummy()
    printf("Hello, World!");
    return 0;
 }
+
+int main()
+{
+   printf("Should never run.");
+   return 1;
+}
 `
 
 module.exports.testFFI = function (test) {