Support "-" as an alias to "/dev/stdout" for the --out parameter

Following the POSIX guideline 13:

> For utilities that use operands to represent files to be opened for
> either reading or writing, the '-' operand should be used only to
> mean
> standard input (or standard output when it is clear from context
> that
> an output file is being specified).

http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap12.html#tag_12_02

See issue microsoft#1226

Author: stroborobo

src/compiler/sys.ts

@@ -355,6 +355,9 @@ namespace ts {
                 if (writeByteOrderMark) {
                     data = "\uFEFF" + data;
                 }
+                if (fileName === "-") {
+                    fileName = "/dev/stdout";
+                }
 
                 let fd: number;