Fix deadlock in timer_delete.

If the callback function for a timer did a timer_delete, the function
would never return. The problem was that the timer_delete function would try
to wait until the timer thread has finished. Waiting for yourself to finish
doesn't work very well.

Bug: 13397340
Change-Id: Ica123a5bafbc8660c8a4a909e5c2dead55ca429d

Conflicts:
	libc/bionic/posix_timers.cpp
Prevent log_backlog to call chk_free

When used with libc_debug_malloc set to 10, log_backlog
might lead to a recursive call to chk_free and lead to a
deadlock when the same thread tries to acquire a second
time the lock backlog_lock.

Change-Id: I71c56463806a44da467bf508e294ff028b716215
Signed-off-by: Jean-Christophe PINCE <jean-christophe.pince@intel.com>
Disable GCOV for bionic

Change-Id: Idc3f0b0fa21b74aa1e611207f879a37a75adf2ee
Fix modf* tests

Use a value that can be exactly represented.

Change-Id: Idf3b1db5e6042fb49c1f591f25f9eee656659ece