Move BACKTRACE_NO_TID to BACKTRACE_CURRENT_THREAD.

Use a bit better name for this. The other name was a bit confusing.

Change-Id: I1261f2ee3854a9c8b82133ad0bfbbbe48b43c9ac

(cherry picked from commit 242b1a8c7a5ec73172bac811e51acbc27201f22c)

Conflicts:
	libbacktrace/Backtrace.cpp
diff --git a/libbacktrace/Backtrace.cpp b/libbacktrace/Backtrace.cpp
index ccfce81..a7568e0 100644
--- a/libbacktrace/Backtrace.cpp
+++ b/libbacktrace/Backtrace.cpp
@@ -219,12 +219,12 @@
 
 Backtrace* Backtrace::Create(pid_t pid, pid_t tid, backtrace_map_info_t* map_info) {
   if (pid == BACKTRACE_CURRENT_PROCESS || pid == getpid()) {
-    if (tid == BACKTRACE_NO_TID || tid == gettid()) {
+    if (tid == BACKTRACE_CURRENT_THREAD || tid == gettid()) {
       return CreateCurrentObj(map_info);
     } else {
       return CreateThreadObj(tid, map_info);
     }
-  } else if (tid == BACKTRACE_NO_TID) {
+  } else if (tid == BACKTRACE_CURRENT_THREAD) {
     return CreatePtraceObj(pid, pid, map_info);
   } else {
     return CreatePtraceObj(pid, tid, map_info);