cmd/ld: set alignment for the .rel.plt section on 32-bit architectures

Fixes #9802.

Change-Id: I22c52a37bdb23a14cc4615c9519431bb14ca81ca
Reviewed-on: https://go-review.googlesource.com/4170Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/ld/elf.c

@@ -1363,6 +1363,7 @@ asmbelf(vlong symo)
 			sh->type = SHT_REL;
 			sh->flags = SHF_ALLOC;
 			sh->entsize = ELF32RELSIZE;
+			sh->addralign = 4;
 			sh->link = elfshname(".dynsym")->shnum;
 			shsym(sh, linklookup(ctxt, ".rel.plt", 0));