Replace hidden_def with libm_hidden_def in math

libm_hidden_def expand the parameters and do not require an extra layer
of macros.
These were the last 3 files in math/ still using hidden_def().

	* math/w_exp_compat.c: Replace hidden_def with libm_hidden_def..
	* math/w_expl_compat.c: Likewise.
	* math/w_exp_template.c: Likewise.  Remove hidden_def_x.

Signed-off-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>