cmd/ld: fix check for address wrap in relocation

PC-relative needs a signed offset; others need unsigned.
Also fix signedness of 32-bit relocation on Windows.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/9039045

src/cmd/ld/data.c

@@ -259,8 +259,7 @@ relocsym(Sym *s)
 			cursym = s;
 			diag("bad reloc size %#ux for %s", siz, r->sym->name);
 		case 4:
-			// TODO: Test is causing breakages on ARM and Windows. Disable for now.
-			if(0 && o != (int32)o) {
+			if((r->type == D_PCREL && o != (int32)o) || (r->type != D_PCREL && o != (uint32)o)) {
 				cursym = S;
 				diag("relocation address is too big: %#llx", o);
 			}

src/cmd/ld/ldpe.c

@@ -291,7 +291,7 @@ ldpe(Biobuf *f, char *pkg, int64 len, char *pn)
 				case IMAGE_REL_AMD64_ADDR32: // R_X86_64_PC32
 				case IMAGE_REL_AMD64_ADDR32NB:
 					rp->type = D_PCREL;
-					rp->add = le32(rsect->base+rp->off);
+					rp->add = (int32)le32(rsect->base+rp->off);
 					break;
 				case IMAGE_REL_I386_DIR32NB:
 				case IMAGE_REL_I386_DIR32: