pr20882 testcase

-gdwarf-sections doesn't work on targets that lack support to emit
address size relative relocs.  The testcase as it was avoided
-gdwarf-sections doing anything by providing a non-empty .debug_line.
It's better to not use -gdwarf-sections.  Also, the testcase failed
to match the output for 16-bit address targets like avr.

	PR ld/20882
	* testsuite/ld-gc/pr20882.d: Don't pass -gdwarf-sections to gas.
	Allow for 16-bit address targets and match expected data fully.
	* testsuite/ld-gc/pr20882a.s: Delete .debug_line section.
	* testsuite/ld-gc/pr20882b.s: Likewise.
	* testsuite/ld-gc/pr20882c.s: Likewise.

ld/ChangeLog

@@ -1,3 +1,12 @@
+2017-05-18  Alan Modra  <amodra@gmail.com>
+
+	PR ld/20882
+	* testsuite/ld-gc/pr20882.d: Don't pass -gdwarf-sections to gas.
+	Allow for 16-bit address targets and match expected data fully.
+	* testsuite/ld-gc/pr20882a.s: Delete .debug_line section.
+	* testsuite/ld-gc/pr20882b.s: Likewise.
+	* testsuite/ld-gc/pr20882c.s: Likewise.
+
 2017-05-17  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR ld/20882

ld/testsuite/ld-gc/pr20882.d

@@ -2,9 +2,8 @@
 #source: pr20882a.s
 #source: pr20882b.s
 #source: pr20882c.s
-#as: -gdwarf-sections
 #ld: --gc-sections -e main
 #readelf: -x .debug_info
 
 #...
- +0x0+ [0-9a-f ]+ 28 +.+\(
+  0x0+ (0a000000 00000000 |00000000 0000000a |06000000 |00000006 |0400|0004)28 .*

ld/testsuite/ld-gc/pr20882a.s

@@ -1,11 +1,8 @@
 	.text
-	.globl  main
-	.type   main, %function
+	.globl	main
+	.type	main, %function
 main:
 	.byte 0
 
 	.section .debug_info,"",%progbits
 	.dc.a  t.c.4903c230+2
-
-	.section .debug_line,"",%progbits
-	.byte 0

ld/testsuite/ld-gc/pr20882b.s

@@ -3,6 +3,3 @@
 	.globl t.c.4903c230
 t.c.4903c230:
 	.byte 0x28
-
-	.section .debug_line,"",%progbits
-	.byte 0

ld/testsuite/ld-gc/pr20882c.s

@@ -3,6 +3,3 @@
 	.globl t.c.4903c231
 t.c.4903c231:
 	.byte   0x29
-
-	.section .debug_line,"",%progbits
-	.byte 0