[mips] Fix local dynamic TLS with Sym64

For the final DTPREL addition, rather than a lui/daddiu/daddu triple,
LLVM was erronously emitting a daddiu/daddiu pair, treating the %dtprel_hi
as if it were a %dtprel_lo, since Mips::Hi expands unshifted for Sym64.
Instead, use a new TlsHi node and, although unnecessary due to the exact
structure of the nodes emitted, use TlsHi for local exec too to prevent
future bugs. Also garbage-collect the unused TprelLo and TlsGd nodes,
and TprelHi since its functionality is provided by the new common TlsHi node.

Patch by James Clarke.

Differential revision: https://reviews.llvm.org/D49259

llvm-svn: 337827
diff --git a/llvm/lib/Target/Mips/MipsISelLowering.h b/llvm/lib/Target/Mips/MipsISelLowering.h
index efb6077..7e5d6a2 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.h
+++ b/llvm/lib/Target/Mips/MipsISelLowering.h
@@ -84,6 +84,9 @@
       // Get the High 16 bits from a 32 bit immediate for accessing the GOT.
       GotHi,
 
+      // Get the High 16 bits from a 32-bit immediate for accessing TLS.
+      TlsHi,
+
       // Handle gp_rel (small data/bss sections) relocation.
       GPRel,