Fix m68k bits/mathinline.h attributes (bug 22631).

Fix m68k bits/mathinline.h attributes (bug 22631).

m68k bits/mathinline.h declares various functions with const
attributes.  These are inappropriate for functions that have results
depending on the rounding mode; the machine-independent
bits/mathcalls.h only uses const attributes for a very few functions
with no rounding mode dependence, and the m68k header should do
likewise.  GCC uses pure for such functions with -frounding-math,
resulting in GCC mainline warning for conflicts with between the
header and the built-in attributes and glibc failing to build for m68k
with GCC mainline.

This patch fixes the attributes to avoid using const except when
bits/mathcalls.h does so.  (There are a few functions where maybe
bits/mathcalls.h could do so but doesn't, but keeping the headers in
sync in this regard seems to be the safe approach.)

Tested compilation with build-many-glibcs.py with GCC mainline.

	[BZ #22631]
	* sysdeps/m68k/m680x0/fpu/bits/mathinline.h (__m81_defun): Add
	argument for attrubutes.  All callers changed.
	(__inline_mathop1): Likewise.  All callers changed.
	(__inline_mathop): Likewise.  All callers changed.
	[__USE_MISC] (scalbn): Use __inline_forward instead of
	__inline_forward_c.
	[__USE_ISOC99] (scalbln): Likewise.
	[__USE_ISOC99] (nearbyint): Likewise.
	[__USE_ISOC99] (lrint): Likewise.
	[__USE_MISC] (scalbnf): Likewise.
	[__USE_ISOC99] (scalblnf): Likewise.
	[__USE_ISOC99] (nearbyintf): Likewise.
	[__USE_ISOC99] (lrintf): Likewise.
	[__USE_MISC] (scalbnl): Likewise.
	[__USE_ISOC99] (scalblnl): Likewise.
	[__USE_ISOC99] (nearbyintl): Likewise.
	[__USE_ISOC99] (lrintl): Likewise.
	* sysdeps/m68k/m680x0/fpu/mathimpl.h: All callers of
	__inline_mathop and __m81_defun changed.