Allow direct use of math_ldbl.h in testsuite.

A few 'long double'-related tests include math_private.h just for
their variety of math_ldbl.h, which contains macros for assembling and
disassembling the binary representation of 'long double'.  math_ldbl.h
insists on being included from math_private.h, but if we relax this
restriction (and fix some portability sloppiness) we can use it
directly and not have to expose all of math_private.h to the testsuite.

	* sysdeps/generic/math_private.h: Use __BIG_ENDIAN and
	__LITTLE_ENDIAN, not BIG_ENDIAN and LITTLE_ENDIAN.

	* sysdeps/generic/math_ldbl.h
	* sysdeps/ia64/fpu/math_ldbl.h
	* sysdeps/ieee754/ldbl-128/math_ldbl.h
	* sysdeps/ieee754/ldbl-128ibm/math_ldbl.h
	* sysdeps/ieee754/ldbl-96/math_ldbl.h
	* sysdeps/powerpc/fpu/math_ldbl.h
	* sysdeps/x86_64/fpu/math_ldbl.h:
	Allow direct inclusion.  Use uintNN_t instead of u_intNN_t.
	Use __BIG_ENDIAN and __LITTLE_ENDIAN, not BIG_ENDIAN and
	LITTLE_ENDIAN.  Include endian.h and/or stdint.h if necessary.
	Add copyright notices.

	* sysdeps/ieee754/ldbl-128ibm/math_ldbl.h (ldbl_canonicalize_int):
	Don't use EXTRACT_WORDS64.

	* sysdeps/ieee754/ldbl-96/test-canonical-ldbl-96.c
	* sysdeps/ieee754/ldbl-96/test-totalorderl-ldbl-96.c
	* sysdeps/ieee754/ldbl-128ibm/test-canonical-ldbl-128ibm.c
	* sysdeps/ieee754/ldbl-128ibm/test-totalorderl-ldbl-128ibm.c:
	Include math_ldbl.h, not math_private.h.