[ld, testsuite] Always assemble those intermediate .o files used later

ld/
	* testsuite/ld-plugin/lto.exp (lto_link_elf_tests): Move "Compile 7",
	"Compile 8a", "Compile 8b"...
	(lto_compile_elf_tests): ...to here.  Always run these tests.
	(lto_run_elf_tests): Move "LTO 7"...
	(lto_run_elf_shared_tests): ...to here.  Restrict these tests on
	environment where share library is supported.

(cherry picked from commit 077c11e8)