egl: link libEGL against the dynamic version of libglapi

Note: the following happens only when using slibtool.
Since this is a very serious breakage, we will keep the workaround until
a better solution is available.

DRI modules store the address of the dispatch table in a TLS variable,
_glapi_tls_Dispatch.

Changes to the way libEGL is built in d884d8d0 resulted in
it being statically linked against libglapi, and thus containing its own
copy of _glapi_tls_Dispatch. The result was that some applications would
fail to work (e.g. deqp-egl, which dynamically loads libEGL), due to the
DRI module storing the dispatch table address in one copy of
_glapi_tls_Dispatch, and libEGL obtaining the address from another copy
of the variable.

Fixes: d884d8d0 "egl/dri: link directly to libglapi.so"
Signed-off-by: Brendan King <Brendan.King@imgtec.com>
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit e491bffc)