8l: do not emit empty dwarf pe sections

This change will allow to generate valid executable,
even if rsc disables dwarf generation, as it happend
at revision 9a64273f9d68.

R=rsc
CC=golang-dev, lvd, vcc
https://golang.org/cl/4425066

src/cmd/ld/dwarf.c

@@ -2567,12 +2567,8 @@ dwarfaddpeheaders(void)
 	newPEDWARFSection(".debug_line", linesize);
 	newPEDWARFSection(".debug_frame", framesize);
 	newPEDWARFSection(".debug_info", infosize);
-	if (pubnamessize > 0)
-		newPEDWARFSection(".debug_pubnames", pubnamessize);
-	if (pubtypessize > 0)
-		newPEDWARFSection(".debug_pubtypes", pubtypessize);
-	if (arangessize > 0)
-		newPEDWARFSection(".debug_aranges", arangessize);
-	if (gdbscriptsize > 0)
-		newPEDWARFSection(".debug_gdb_scripts", gdbscriptsize);
+	newPEDWARFSection(".debug_pubnames", pubnamessize);
+	newPEDWARFSection(".debug_pubtypes", pubtypessize);
+	newPEDWARFSection(".debug_aranges", arangessize);
+	newPEDWARFSection(".debug_gdb_scripts", gdbscriptsize);
 }

src/cmd/ld/pe.c

@@ -415,6 +415,9 @@ newPEDWARFSection(char *name, vlong size)
 	IMAGE_SECTION_HEADER *h;
 	char s[8];
 
+	if(size == 0)
+		return nil;
+
 	if(nextsymoff+strlen(name)+1 > sizeof(symnames)) {
 		diag("pe string table is full");
 		errorexit();