buildroot

Add a config option for gcc tls support, rather than disabling it blindly

Defaulted to yes, but blocked it from gcc 4.4.x since the disable was
originally added because of problems with its c++ support reportedly.

Signed-off-by: Austin Foxley <austinf@cetoncorp.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>