math: Fix i386 and m68k exp10 on static build (BZ 31775)

The commit 08ddd268 removed the static exp10 on i386 and m68k with an
empty w_exp10.c (required for the ABIs that uses the newly
implementation).  This patch fixes by adding the required symbols on the
arch-specific w_exp{f}_compat.c implementation.

Checked on i686-linux-gnu and with a build for m68k-linux-gnu.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>