ld/testsuite: prepare ld-elfvsb to support XCOFF

A following patch will add visibility support in ld for XCOFF. Thus,
ld-elfvsb is renamed ld-vsb and a suffix is added to files targeting only
ELF format.

ld/ChangeLog:

	* testsuite/ld-elfvsb: rename as ld-vsb.
	* testsuite/ld-elfvsb/hidden0.d: move to ld-vsb and rename with
	  suffix -elf.d.
	* testsuite/ld-elfvsb/hidden1.d: Likewise.
	* testsuite/ld-elfvsb/hidden2.d: Likewise.
	* testsuite/ld-elfvsb/internal0.d: Likewise.
	* testsuite/ld-elfvsb/internal1.d: Likewise.
	* testsuite/ld-elfvsb/protected0.d: Likewise.
	* testsuite/ld-elfvsb/protected1.d: Likewise.

ld/testsuite/ld-vsb/vsb.exp

@@ -49,7 +49,7 @@ if { ![istarget hppa*64*-*-hpux*] \
     return
 }
 
-set test_list [lsort [glob -nocomplain $srcdir/$subdir/*.d]]
+set test_list [lsort [glob -nocomplain $srcdir/$subdir/*-elf.d]]
 foreach t $test_list {
     # We need to strip the ".d", but can leave the dirname.
     verbose [file rootname $t]