Use $(rtld-prefix) more consistently.

The glibc makefiles have a standard variable, $(rtld-prefix), to run
the dynamic linker with a default --library-path option; this is used
as the basis of lots of other variables for running programs compiled
with the newly built library.

A few places however use $(elf-objpfx)ld.so or
$(elf-objpfx)${rtld-installed-name} directly, with such a
--library-path option.  This patch makes such places use
$(rtld-prefix) instead.  I'm not aware of any significance in these
cases to the choice of ld.so or ${rtld-installed-name} when running
the dynamic linker, or to whether $(patsubst
%,:%,$(sysdep-library-path)) is included in the library-path as it is
in $(rtld-prefix) and just one of the places being changed.

Tested x86_64.

	* elf/Makefile ($(objpfx)tst-unused-dep.out): Use $(rtld-prefix).
	* iconvdata/Makefile ($(inst_gconvdir)/gconv-modules)
	[$(cross-compiling) = no]: Likewise.
	* sysdeps/s390/s390-64/Makefile ($(inst_gconvdir)/gconv-modules)
	[$(cross-compiling) = no]: Likewise.

localedata/ChangeLog:
	* Makefile (LOCALEDEF): Use $(rtld-prefix).
Don't read past end of pattern in fnmatch (BZ #17062)
Fix __ieee754_logl (-LDBL_MAX) in FE_DOWNWARD mode (bug 17022).

This patch fixes __ieee754_logl (-LDBL_MAX) on x86_64 and x86 not to
subtract 1 from its argument and so cause spurious overflow in
FE_DOWNWARD mode.  (For any argument strictly less than -1, it doesn't
matter whether or not 1 is subtracted before computing log1p, as long
as the result doesn't overflow to -Inf.)

Tested x86_64 and x86.  (This particular case lacks test coverage,
since the testsuite doesn't cover -lieee, but it will be covered by
tests after the following patch to test pow in all rounding modes,
which was the context in which this bug was found.)

	[BZ #17022]
	* sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Do not subtract 1
	from arguments -2 or below.
	* sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise.
	* sysdeps/x86_64/fpu/e_logl.S (__ieee754_logl): Likewise.