Add a Musl environment to the triple.

It will be used in clang.

Patch by Lei Zhang.

llvm-svn: 272660
diff --git a/llvm/unittests/ADT/TripleTest.cpp b/llvm/unittests/ADT/TripleTest.cpp
index e383542..c860222 100644
--- a/llvm/unittests/ADT/TripleTest.cpp
+++ b/llvm/unittests/ADT/TripleTest.cpp
@@ -93,6 +93,12 @@
   EXPECT_EQ(Triple::Linux, T.getOS());
   EXPECT_EQ(Triple::GNU, T.getEnvironment());
 
+  T = Triple("x86_64-pc-linux-musl");
+  EXPECT_EQ(Triple::x86_64, T.getArch());
+  EXPECT_EQ(Triple::PC, T.getVendor());
+  EXPECT_EQ(Triple::Linux, T.getOS());
+  EXPECT_EQ(Triple::Musl, T.getEnvironment());
+
   T = Triple("powerpc-bgp-linux");
   EXPECT_EQ(Triple::ppc, T.getArch());
   EXPECT_EQ(Triple::BGP, T.getVendor());