M680x0-llvm should understand the m68k-*-*-* triplet

[glaubitz]

While working on the Rust backend for m68k based on the M680x0-llvm project, I ran into the problem that the LLVM target m68k-unknown-linux-gnu as I used in [1] was not understood by M680x0-llvm.

Since m68k-*-*-* is the common and widely used triplet name for m68k on Linux and other operating systems, I suggest the following change to the triplet code so that the logic matches the one for SystemZ/s390x:

diff --git a/lib/Support/Triple.cpp b/lib/Support/Triple.cpp
index aea18102646..71017cb8daf 100644
--- a/lib/Support/Triple.cpp
+++ b/lib/Support/Triple.cpp
@@ -69,7 +69,7 @@ StringRef Triple::getArchTypeName(ArchType Kind) {
   case shave:          return "shave";
   case wasm32:         return "wasm32";
   case wasm64:         return "wasm64";
-  case m680x0:         return "m680x0";
+  case m680x0:         return "m68k";
   case renderscript32: return "renderscript32";
   case renderscript64: return "renderscript64";
   }
@@ -391,7 +391,7 @@ static Triple::ArchType parseArch(StringRef ArchName) {
     .Cases("powerpc", "ppc", "ppc32", Triple::ppc)
     .Cases("powerpc64", "ppu", "ppc64", Triple::ppc64)
     .Cases("powerpc64le", "ppc64le", Triple::ppc64le)
-    .Case("m680x0", Triple::m680x0)
+    .Cases("m680x0", "m68k", Triple::m680x0)
     .Case("xscale", Triple::arm)
     .Case("xscaleeb", Triple::armeb)
     .Case("aarch64", Triple::aarch64)

[1] https://github.com/glaubitz/rust/blob/m68k-linux/src/librustc_target/spec/m68k_unknown_linux_gnu.rs