`./configure` falsely claims that compiler doesn't support -fsanitize=thread
$ gcc --version
gcc (Debian 4.9.2-10) 4.9.2
$ ./configure --enable-fsanitize-tsan
...
checking whether C compiler handles -fsanitize=thread... no
...
CFLAGS from ./configure output doesn't include -fsanitize=thread
But gcc 4.9.2 manual says it does support -fsanitize=thread