As the TLS work progress, the convention used by drivers to get the pointer to the current dispatch table from libGL changes. In single-threaded mode, the variable _glapi_DispatchTSD holds a pointer to the dispatch table. In multi-threaded mode, that variable is NULL, and the function _glapi_get_dispatch must be called. In order to support older versions of libGL (i.e., ones that don't have _glapi_DispatchTSD) an ELF "weak" symbol was added to dri_util.c. For drivers built in the Mesa tree, this symbol shows up, as weak, in the *_dri.so files. However, the *_dri.so files built in the DRI don't have it. The net result is these drivers won't work with, for example, the libGL from the current Xorg tree. I suspect that the problem is just the options passed to gcc when the *_dri.so is linked.
The weak version of _glapi_DispatchTSD was removed from dri_util.c. As stated in the bug report, this was only needed to support versions of libGL that did not have this symbol. Versions of libGL without this symbol are no longer supported at all, so it is totally irrelevant.
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