Add --gc-sections test checking removal of __start/__stop symbols.

Well, just __stop__foo but that should be good enough.

	* testsuite/ld-gc/stop.d,
	* testsuite/ld-gc/stop.s: New test.
	* testsuite/ld-gc/gc.exp: Run it.

ld/ChangeLog

@@ -1,3 +1,9 @@
+2018-01-30  Alan Modra  <amodra@gmail.com>
+
+	* testsuite/ld-gc/stop.d,
+	* testsuite/ld-gc/stop.s: New test.
+	* testsuite/ld-gc/gc.exp: Run it.
+
 2018-01-30  Maciej W. Rozycki  <macro@mips.com>
 
 	PR ld/22649

ld/testsuite/ld-gc/gc.exp

@@ -104,6 +104,7 @@ test_gc "Check --gc-section/-r/-u" "gcrel" $ld "-r --gc-sections -u used_func"
 run_dump_test "noent"
 run_dump_test "abi-note"
 run_dump_test "start"
+run_dump_test "stop"
 run_dump_test "pr19167"
 if { [is_elf_format] } then {
     run_dump_test "all-debug-sections"

ld/testsuite/ld-gc/stop.d

@@ -0,0 +1,10 @@
+#name: --gc-sections removing __stop_
+#ld: --gc-sections -e _start
+#nm: -n
+#target: *-*-linux* *-*-gnu*
+#notarget: *-*-*aout *-*-*oldld frv-*-linux* metag-*-linux*
+
+#failif
+#...
+[0-9a-f]+ D +__stop__foo
+#...

ld/testsuite/ld-gc/stop.s

@@ -0,0 +1,8 @@
+	.text
+	.globl _start
+_start:
+	.dc.a	0
+
+	.section	_foo,"aw",%progbits
+foo:
+	.long	1