s390: Do not replace brcth referencing undefined weak symbol

Branch Relative on Count High (brcth) is a conditional branch relative
instruction. It is not guaranteed that it only appears within loops
that sooner or later will take the branch. It may very well be used to
check a condition that will prevent the branch from ever being taken.

bfd/
	* elf64-s390.c (elf_s390_relocate_section): Do not replace brcth
	referencing undefined weak symbol with a trap.

ld/
	* testsuite/ld-s390/weakundef-1.s: Update test case accordingly.
	* testsuite/ld-s390/weakundef-1.dd: Likewise.

Fixes: 896a639bab ("s390: Avoid reloc overflows on undefined weak symbols")
Signed-off-by: Jens Remus <jremus@linux.ibm.com>

bfd/elf64-s390.c

@@ -2517,10 +2517,9 @@ elf_s390_relocate_section (bfd *output_bfd,
 		 - store halfword relative long (sthrl)
 		 - execute relative long (exrl)
 		 - compare (logical) relative long (crl, clrl, cgrl, clgrl, cgfrl, clgfrl)
-		 - compare (logical) halfword relative long (chrl, cghrl, clhrl, clghrl)
-		 - branch relative on count high (brcth)  */
+		 - compare (logical) halfword relative long (chrl, cghrl, clhrl, clghrl)  */
 	      else if (op == 0xc005 || (op & 0xff00) == 0xc400
-		       || (op & 0xff00) == 0xc600 || op == 0xcc06)
+		       || (op & 0xff00) == 0xc600)
 		{
 		  /* Emit a 6-byte trap: jg .+2  */
 		  bfd_put_16 (output_bfd, 0xc0f4, insn_start);

ld/testsuite/ld-s390/weakundef-1.dd

@@ -3,13 +3,13 @@ tmpdir/weakundef-1:     file format elf64-s390
 Disassembly of section .text:
 
 .* <foo>:
-.*:	c0 10 00 00 00 1e [	 ]*larl	%r1,20000003c <d>
-.*:	c0 10 00 00 00 1f [	 ]*larl	%r1,200000044 <wd>
+.*:	c0 10 00 00 00 1c [	 ]*larl	%r1,200000038 <d>
+.*:	c0 10 00 00 00 1d [	 ]*larl	%r1,200000040 <wd>
 .*:	e3 10 00 00 00 71 [	 ]*lay	%r1,0
 .*:	c0 f4 00 00 00 01 [	 ]*jg	.*
 .*:	c0 f4 00 00 00 01 [	 ]*jg	.*
 .*:	c0 f4 00 00 00 01 [	 ]*jg	.*
 .*:	c0 f4 00 00 00 01 [	 ]*jg	.*
 .*:	c0 f4 00 00 00 01 [	 ]*jg	.*
-.*:	c0 f4 00 00 00 01 [	 ]*jg	.*
 .*:	c0 04 00 00 00 00 [	 ]*jgnop	.*
+.*:	07 07 [	 ]*nopr	%r7

ld/testsuite/ld-s390/weakundef-1.s

@@ -9,7 +9,6 @@ foo:
 	lrl	%r1,wu
 	strl	%r1,wu
 	exrl	%r1,wu
-	brcth	%r1,wu
 	pfdrl	%r1,wu
 	.weak	wd
 	.weak	wu