8l: fix windows build.

R=rsc, brainman
CC=golang-dev
https://golang.org/cl/2543042

src/cmd/ld/pe.c

@@ -96,6 +96,7 @@ pewrite(void)
 	for (i=0; i<nsect; i++)
 		for (j=0; j<sizeof(sh[i]); j++)
 			cput(((char*)&sh[i])[j]);
+	strnput("", PERESERVE-0x400);
 }
 
 void

src/cmd/ld/pe.h

@@ -72,8 +72,8 @@ typedef struct {
 	uint32 FirstThunk;
 } IMAGE_IMPORT_DESCRIPTOR;
 
-#define PERESERVE	0x400
-#define PEALIGN		0x200
+#define PERESERVE	0x1000
+#define PEALIGN		0x1000
 #define PEBASE		0x00400000
 
 enum {