LD/testsuite: Move ELF shared library tests from elf.exp to shared.exp

Move those ELF shared library tests that are in ld-elf/elf.exp over to
ld-elf/shared.exp, to keep them all together and make the maintenance of
extra flags needed with some targets and shared library builds easier,
and also removing the need for the large:

if { [check_shared_lib_support] } then {
    [...]
}

conditional block and consequently reducing indentation, which always
helps with TCL code.  No functional change, except for the order of
individual test case execution which has changed accordingly, i.e. the
test results are shuffled.

	ld/
	* testsuite/ld-elf/elf.exp: Move shared library tests over to...
	* testsuite/ld-elf/shared.exp: ... here.