syslog-ng: fix do_compi1e of qemuarm while DEBUG_BUILD

The thread local storage caused arm-gcc broken while compiling
syslog-ng with option '-g -O'.
...
dnscache.s: Assembler messages:
dnscache.s:100: Error: invalid operands (.text and *UND* sections) for `-'
...

Add option --enable-thread-tls in configure to explicitly disable
thread local storage for arm while DEBUG_BUILD enabled.

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>