Convert futex to cond wait.

Switch to the better supported pthread_cond to handle the Wait/Wake
functions.

Also, increase the number of simultaneous threads in the thread tests.

Bug: 18381207

(cherry picked from commit db44538387b08f367fc2419653639866f4c2fbd6)

Change-Id: Id326a7a7b92cb61573def3f761597c40f3ef2f4b
diff --git a/libbacktrace/Android.mk b/libbacktrace/Android.mk
index 01b4f4d..f2f71f9 100755
--- a/libbacktrace/Android.mk
+++ b/libbacktrace/Android.mk
@@ -64,6 +64,10 @@
 libbacktrace_static_libraries_host := \
 	libcutils \
 
+libbacktrace_ldlibs_host := \
+	-lpthread \
+	-lrt \
+
 module := libbacktrace
 module_tag := optional
 build_type := target