add mipsel-unknown-none target

Author: kiffie

src/doc/rustc/src/platform-support.md

@@ -180,6 +180,7 @@ target | std | host | notes
 `i686-wrs-vxworks` | ? |  |
 `mips-unknown-linux-uclibc` | ✓ |  | MIPS Linux with uClibc
 `mipsel-unknown-linux-uclibc` | ✓ |  | MIPS (LE) Linux with uClibc
+`mipsel-unknown-none` | * |  | Bare MIPS (LE) softfloat
 `mipsel-sony-psp` | * |  | MIPS (LE) Sony PlayStation Portable (PSP)
 `mipsisa32r6-unknown-linux-gnu` | ? |  |
 `mipsisa32r6el-unknown-linux-gnu` | ? |  |