[6716aa8] Force use of TLS if heap profiling is enabled

[Jason Evans]

On Apr 23, 2012, at 11:35 PM, Mike Hommey wrote:
> Out of curiosity, what makes heap profiling require __thread?
> (I'm curious because it makes it unusable on OSX and Windows)

There's a bunch of per thread state that is needed to keep the profiling code from becoming a contention point.  It's probably possible to refactor the code to avoid the dependency on __thread (make tsd allocation safe), but right now there are other reasons heap profiling only works on Linux (e.g. "/proc/self/maps"), so for now I chose to modify the configure script to prevent an unusable configuration.

Jason