elf: Check symbol version without any symbols

VER_FLG_WEAK doesn't indicate that all symbol references of the symbol
version have STB_WEAK.  VER_FLG_WEAK indicates a weak symbol version
definition with no symbols associated with it.  It is used to verify
the existence of a particular implementation without any symbol references
to the weak symbol version.

	PR ld/24718
	* testsuite/ld-elf/pr24718-1.d: New file.
	* testsuite/ld-elf/pr24718-1.s: Likewise.
	* testsuite/ld-elf/pr24718-1.t: Likewise.

ld/testsuite/ld-elf/pr24718-1.d

@@ -0,0 +1,13 @@
+#ld: -shared -version-script pr24718-1.t
+#readelf: -V
+#target: [check_shared_lib_support]
+#xfail: hppa64-*-* tic6x-*-*
+# hppa64 uses dot-symbols, tic6x requires a non-default emulation.
+
+#...
+Version definition section '\.gnu\.version_d' contains 3 entries:
+ +Addr: 0x[0-9a-f]+ +Offset: 0x[0-9a-f]+ +Link: [0-9]+ \(\.dynstr\)
+ +000000: Rev: 1 +Flags: BASE +Index: 1 +Cnt: 1 +Name: dump
+ +0x001c: Rev: 1 +Flags: WEAK +Index: 2 +Cnt: 1 +Name: FOO_DEP
+ +0x0038: Rev: 1 +Flags: none +Index: 3 +Cnt: 1 +Name: FOO
+#pass

ld/testsuite/ld-elf/pr24718-1.s

@@ -0,0 +1,7 @@
+	.text
+	.globl foo
+	.globl foo
+	.type foo,%function
+foo:
+	.byte 0
+	.size foo, 1

ld/testsuite/ld-elf/pr24718-1.t

@@ -0,0 +1,4 @@
+FOO_DEP { };
+FOO {
+  foo;
+};