Include most of elf/ modules-names in modules-names-tests

  I'm testing a patch to let the compiler expand calls to floor in libm
as built-in function calls as much as possible, instead of calling
__floor, so that no architecture-specific __floor inlines are needed,
and then to arrange for non-inlined calls to end up calling __floor,
as done with sqrt and __ieee754_sqrt.

This shows up elf/tst-relsort1mod2.c calling floor, which must not be
converted to a call to __floor.  Now, while an IS_IN (libm)
conditional could be added to the existing conditionals on such
redirections in include/math.h, the _ISOMAC conditional ought to
suffice (code in other glibc libraries shouldn't be calling floor or
sqrt anyway, as they aren't provided in libc and the other libraries
don't link with libm).  But while tests are mostly now built with
_ISOMAC defined, test modules in modules-names aren't unless also
listed in modules-names-tests.

As far as I can see, all the modules in modules-names in elf/ are in
fact parts of tests and so listing them in modules-names-tests is
appropriate, so they get built with something closer to the headers
used for user code, except in a few cases that actually rely on
something from internal headers.  This patch duly sets
modules-names-tests there accordingly (filtering out those tests that
fail to build without internal headers).

Tested for x86_64.

2018-09-11  Joseph Myers  <joseph@codesourcery.com>

	* elf/Makefile (modules-names-tests): New variable.