Dwarf backtrace for MIPS

The Dwarf parsing code was copied from backtrace-x86.c
and modified for MIPS

Change-Id: I62c698fbbea28be39320a921dd778269dc478528
diff --git a/libcorkscrew/ptrace-arch.h b/libcorkscrew/ptrace-arch.h
index 4451c29..0bcff63 100755
--- a/libcorkscrew/ptrace-arch.h
+++ b/libcorkscrew/ptrace-arch.h
@@ -33,6 +33,8 @@
 #ifdef __arm__
     uintptr_t exidx_start;
     size_t exidx_size;
+#elif __mips__
+    uintptr_t eh_frame_hdr;
 #elif __i386__
     uintptr_t eh_frame_hdr;
 #endif