Make scalbn set errno (bug 6803).

Make scalbn set errno (bug 6803).

As noted in bug 6803, scalbn fails to set errno on overflow and
underflow.  This patch fixes this by making scalbn an alias of ldexp,
which has exactly the same semantics (for floating-point types with
radix 2) and already has wrappers that deal with setting errno,
instead of an alias of the internal __scalbn (which ldexp calls).

Notes:

* Where compat symbols were defined for scalbn functions, I didn't
  change what they point to (to keep the patch minimal), so such
  compat symbols continue to go directly to the non-errno-setting
  functions.

* Mike, I didn't do anything with the IA64 versions of these
  functions, where I think both the ldexp and scalbn functions already
  deal with setting errno.  As a cleanup (not needed to fix this bug)
  however you might want to make those functions into aliases for
  IA64; there is no need for them to be separate function
  implementations at all.

* This concludes the fix for bug 6803 since the scalb and scalbln
  cases of that bug were fixed some time ago.

Tested for x86_64, x86, mips64 and powerpc.

	[BZ #6803]
	* math/s_ldexp.c (scalbn): Define as weak alias of __ldexp.
	[NO_LONG_DOUBLE] (scalbnl): Define as weak alias of __ldexp.
	* math/s_ldexpf.c (scalbnf): Define as weak alias of __ldexpf.
	* math/s_ldexpl.c (scalbnl): Define as weak alias of __ldexpl.
	* sysdeps/i386/fpu/s_scalbn.S (scalbn): Remove alias.
	* sysdeps/i386/fpu/s_scalbnf.S (scalbnf): Likewise.
	* sysdeps/i386/fpu/s_scalbnl.S (scalbnl): Likewise.
	* sysdeps/ieee754/dbl-64/s_scalbn.c (scalbn): Likewise.
	[NO_LONG_DOUBLE] (scalbnl): Likewise.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_scalbn.c (scalbn):
	Likewise.
	[NO_LONG_DOUBLE] (scalbnl): Likewise.
	* sysdeps/ieee754/flt-32/s_scalbnf.c (scalbnf): Likewise.
	* sysdeps/ieee754/ldbl-128/s_scalbnl.c (scalbnl): Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_scalbnl.c (scalbnl): Remove
	long_double_symbol calls.
	* sysdeps/ieee754/ldbl-64-128/s_scalbnl.c (scalbnl): Likewise.
	* sysdeps/ieee754/ldbl-opt/s_ldexpl.c (__ldexpl_2): Define as
	strong alias of __ldexpl.
	(scalbnl): Define using long_double_symbol.
	* sysdeps/m68k/m680x0/fpu/s_scalbn.c (__CONCATX(scalbn,suffix)):
	Remove alias.
	* sysdeps/sparc/sparc64/soft-fp/s_scalbnl.c (scalbnl): Likewise.
	* sysdeps/x86_64/fpu/s_scalbnl.S (scalbnl): Likewise.
	* math/libm-test.inc (scalbn_test_data): Add errno expectations.
	(scalbln_test_data): Add more errno expectations.