cmd/link: support R_PPC_REL32 relocation

This relocation is found in libgcc.a in the .eh_frame, and therefore
needs to be handled when doing an internal link.

Fixes #13375.

Change-Id: Idd9e8178e08851a101b43261a30939bcfaf394f9
Reviewed-on: https://go-review.googlesource.com/17173
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

src/cmd/link/internal/ld/ldelf.go

@@ -1159,7 +1159,8 @@ func reltype(pn string, elftype int, siz *uint8) int {
 		'8' | R_386_GOTOFF<<24,
 		'8' | R_386_GOTPC<<24,
 		'8' | R_386_GOT32X<<24,
-		'9' | R_PPC64_REL24<<24:
+		'9' | R_PPC64_REL24<<24,
+		'9' | R_PPC_REL32<<24:
 		*siz = 4
 
 	case '6' | R_X86_64_64<<24,

src/cmd/link/internal/ppc64/asm.go

@@ -296,6 +296,16 @@ func adddynrel(s *ld.LSym, r *ld.Reloc) {
 
 		return
 
+	case 256 + ld.R_PPC_REL32:
+		r.Type = obj.R_PCREL
+		r.Add += 4
+
+		if targ.Type == obj.SDYNIMPORT {
+			ld.Diag("unexpected R_PPC_REL32 for dyn import")
+		}
+
+		return
+
 	case 256 + ld.R_PPC64_ADDR64:
 		r.Type = obj.R_ADDR
 		if targ.Type == obj.SDYNIMPORT {