gas: Fix checking for backwards .org with negative offset

This patch fixes internal errors in (at least) arm and aarch64 GAS
when assembling code that attempts a negative .org.  The bug appears
to be a regression introduced in binutils-2.29 by commit 9875b36538.

	* write.c (relax_segment): Fix handling of negative offset when
	relaxing an rs_org frag.
	* testsuite/gas/aarch64/org-neg.d: New test.
	* testsuite/gas/aarch64/org-neg.l: Error output for test.
	* testsuite/gas/aarch64/org-neg.s: Input for test.
	* testsuite/gas/arm/org-neg.d: New test.
	* testsuite/gas/arm/org-neg.l: Error output for test.
	* testsuite/gas/arm/org-neg.s: Input for test.

gas/ChangeLog

@@ -1,3 +1,14 @@
+2020-06-01  Alex Coplan  <alex.coplan@arm.com>
+
+	* write.c (relax_segment): Fix handling of negative offset when
+	relaxing an rs_org frag.
+	* testsuite/gas/aarch64/org-neg.d: New test.
+	* testsuite/gas/aarch64/org-neg.l: Error output for test.
+	* testsuite/gas/aarch64/org-neg.s: Input for test.
+	* testsuite/gas/arm/org-neg.d: New test.
+	* testsuite/gas/arm/org-neg.l: Error output for test.
+	* testsuite/gas/arm/org-neg.s: Input for test.
+
 2020-05-28  Stephen Casner  <casner@acm.org>
 
 	Fix unexpected failures in gas testsuite for pdp11-aout target.

gas/testsuite/gas/aarch64/org-neg.d

@@ -0,0 +1,3 @@
+#name: negative org should not cause internal error
+#source: org-neg.s
+#error_output: org-neg.l

gas/testsuite/gas/aarch64/org-neg.l

@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+.*: Error: attempt to move .org backwards

gas/testsuite/gas/aarch64/org-neg.s

@@ -0,0 +1,2 @@
+.=-1
+ret

gas/testsuite/gas/arm/org-neg.d

@@ -0,0 +1,3 @@
+#name: negative org should not cause internal error
+#source: org-neg.s
+#error_output: org-neg.l

gas/testsuite/gas/arm/org-neg.l

@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+.*: Error: attempt to move .org backwards

gas/testsuite/gas/arm/org-neg.s

@@ -0,0 +1,2 @@
+.=-1
+nop

gas/write.c

@@ -2940,7 +2940,7 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
 
 	      case rs_org:
 		{
-		  addressT target = offset;
+		  offsetT target = offset;
 		  addressT after;
 
 		  if (symbolP)
@@ -2960,7 +2960,7 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
 		  /* Growth may be negative, but variable part of frag
 		     cannot have fewer than 0 chars.  That is, we can't
 		     .org backwards.  */
-		  if (address + fragP->fr_fix > target)
+		  if ((offsetT) (address + fragP->fr_fix) > target)
 		    {
 		      growth = 0;