please review: tiny addition addition to elf headers for mips16

[Reed Kotler]

I'm not authorized to put back to areas outside of mips without approval.

gas places flags for mips16 and o32 abi into the header, in addition to 
the normal mips32r2

Mips16 is an application specific extension (ASE) to Mips32 .
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diff --git a/include/llvm/Support/ELF.h b/include/llvm/Support/ELF.h
index 2c831a6..f2cce5d 100644
--- a/include/llvm/Support/ELF.h
+++ b/include/llvm/Support/ELF.h
@@ -748,7 +748,10 @@ enum {
   EF_MIPS_ARCH_32R2 = 0x70000000, // mips32r2
   EF_MIPS_ARCH_64R2 = 0x80000000, // mips64r2
   EF_MIPS_ARCH      = 0xf0000000, // Mask for applying EF_MIPS_ARCH_ variant
-  EF_MIPS_MICROMIPS = 0x02000000  // microMIPS
+  EF_MIPS_MICROMIPS = 0x02000000, // microMIPS
+  EF_MIPS_ARCH_ASE_M16 =
+                      0x04000000, // Has Mips-16 ISA extensions
+  E_MIPS_ABI_O32 =    0x00001000  // Original O32
 };
 
 // ELF Relocation types for Mips