Refactor FP_ILOGB* out of bits/mathdef.h.

Continuing the refactoring of bits/mathdef.h, this patch stops it
defining FP_ILOGB0 and FP_ILOGBNAN, moving the required information to
a new header bits/fp-logb.h.

There are only two possible values of each of those macros permitted
by ISO C.  TS 18661-1 adds corresponding macros for llogb, and their
values are required to correspond to those of the ilogb macros in the
obvious way.  Thus two boolean values - for which the same choices are
correct for most architectures - suffice to determine the value of all
these macros, and by defining macros for those boolean values in
bits/fp-logb.h we can then define the public FP_* macros in math.h and
avoid the present duplication of the associated feature test macro
logic.

This patch duly moves to bits/fp-logb.h defining __FP_LOGB0_IS_MIN and
__FP_LOGBNAN_IS_MIN.  Default definitions of those to 0 are correct
for both architectures, while ia64, m68k and x86 get their own
versions of bits/fp-logb.h to reflect their use of values different
from the defaults.

The patch renders many copies of bits/mathdef.h trivial (needed only
to avoid the default __NO_LONG_DOUBLE_MATH).  I'll revise
<https://sourceware.org/ml/libc-alpha/2016-11/msg00865.html>
accordingly so that it removes all bits/mathdef.h headers except the
default one and the alpha one, and arranges for the header to be
included only by complex.h as the only remaining use at that point
will be for the alpha ABI issues there.

Tested for x86_64 and x86.  Also did compile-only testing with
build-many-glibcs.py (using glibc sources from before the commit that
introduced many build failures with undefined __GI___sigsetjmp).

	* bits/fp-logb.h: New file.
	* sysdeps/ia64/bits/fp-logb.h: Likewise.
	* sysdeps/m68k/m680x0/bits/fp-logb.h: Likewise.
	* sysdeps/x86/bits/fp-logb.h: Likewise.
	* math/Makefile (headers): Add bits/fp-logb.h.
	* math/math.h: Include <bits/fp-logb.h>.
	[__USE_ISOC99] (FP_ILOGB0): Define based on __FP_LOGB0_IS_MIN.
	[__USE_ISOC99] (FP_ILOGBNAN): Define based on __FP_LOGBNAN_IS_MIN.
	* bits/mathdef.h (FP_ILOGB0): Remove.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/aarch64/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/alpha/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/ia64/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/m68k/m680x0/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/mips/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/powerpc/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/s390/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/sparc/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.
	* sysdeps/x86/bits/mathdef.h (FP_ILOGB0): Likewise.
	(FP_ILOGBNAN): Likewise.

2 files changed, 24 insertions, 9 deletions

diff --git a/sysdeps/m68k/m680x0/bits/fp-logb.h b/sysdeps/m68k/m680x0/bits/fp-logb.h
new file mode 100644
index 0000000000..8ece1265c9
--- /dev/null
+++ b/sysdeps/m68k/m680x0/bits/fp-logb.h
@@ -0,0 +1,24 @@
+/* Define __FP_LOGB0_IS_MIN and __FP_LOGBNAN_IS_MIN.  M68K version.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _MATH_H
+# error "Never use <bits/fp-logb.h> directly; include <math.h> instead."
+#endif
+
+#define __FP_LOGB0_IS_MIN	1
+#define __FP_LOGBNAN_IS_MIN	0
diff --git a/sysdeps/m68k/m680x0/bits/mathdef.h b/sysdeps/m68k/m680x0/bits/mathdef.h
index 702bd0e33a..7926c6aaf7 100644
--- a/sysdeps/m68k/m680x0/bits/mathdef.h
+++ b/sysdeps/m68k/m680x0/bits/mathdef.h
@@ -18,12 +18,3 @@
 #if !defined _MATH_H && !defined _COMPLEX_H
 # error "Never use <bits/mathdef.h> directly; include <math.h> instead"
 #endif
-
-#if defined __USE_ISOC99 && defined _MATH_H && !defined _MATH_H_MATHDEF
-# define _MATH_H_MATHDEF	1
-
-/* The values returned by `ilogb' for 0 and NaN respectively.  */
-# define FP_ILOGB0	(-2147483647 - 1)
-# define FP_ILOGBNAN	(2147483647)
-
-#endif	/* ISO C99 */