Support mips(el)-unknown-linux-musl (#562)

* Add: mips(el) musl support

* Fix: musl not gnu

Author: gbusker

src/lib.rs

@@ -2352,7 +2352,9 @@ impl Build {
             "i686-unknown-linux-musl" => Some("musl"),
             "i686-unknown-netbsd" => Some("i486--netbsdelf"),
             "mips-unknown-linux-gnu" => Some("mips-linux-gnu"),
+            "mips-unknown-linux-musl" => Some("mips-linux-musl"),
             "mipsel-unknown-linux-gnu" => Some("mipsel-linux-gnu"),
+            "mipsel-unknown-linux-musl" => Some("mipsel-linux-musl"),
             "mips64-unknown-linux-gnuabi64" => Some("mips64-linux-gnuabi64"),
             "mips64el-unknown-linux-gnuabi64" => Some("mips64el-linux-gnuabi64"),
             "mipsisa32r6-unknown-linux-gnu" => Some("mipsisa32r6-linux-gnu"),