uclibc-ng: remove temporary workaround

fminf and others got implemented in the time after this
patch was added. Remove the workaround to get mesa compiled
with uClibc-ng.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>