Issue error if compiling for multiple targets and program is coming from stdin.

We currently don't support this, so at least now we issue an intelligible error
message in this case.

Issue #269.

module.cpp

@@ -2199,6 +2199,12 @@ Module::CompileAndOutput(const char *srcFile,
                   "compiling C++ output.");
             return 1;
         }
+        if (srcFile == NULL || !strcmp(srcFile, "-")) {
+            Error(SourcePos(), "Compiling programs from standard input isn't "
+                  "supported when compiling for multiple targets.  Please use "
+                  "an intermediate temporary file.");
+            return 1;
+        }
 
         // The user supplied multiple targets
         std::vector<std::string> targets = lExtractTargets(target);