8l/6l: new -Hwindowsgui flag allows to build windows gui pe

Fixes #1516.

R=rsc, mattn
CC=golang-dev
https://golang.org/cl/4214041

src/cmd/6l/obj.c

@@ -51,6 +51,7 @@ Header headers[] = {
    "linux", Hlinux,
    "freebsd", Hfreebsd,
    "windows", Hwindows,
+   "windowsgui", Hwindows,
    0, 0
 };
 

src/cmd/8l/obj.c

@@ -57,6 +57,7 @@ Header headers[] = {
    "nacl", Hnacl,
    "freebsd", Hfreebsd,
    "windows", Hwindows,
+   "windowsgui", Hwindows,
    "tiny", Htiny,
    0, 0
 };

src/cmd/ld/lib.c

@@ -1271,8 +1271,10 @@ headtype(char *name)
 	int i;
 
 	for(i=0; headers[i].name; i++)
-		if(strcmp(name, headers[i].name) == 0)
+		if(strcmp(name, headers[i].name) == 0) {
+			headstring = headers[i].name;
 			return headers[i].val;
+		}
 	fprint(2, "unknown header type -H %s\n", name);
 	errorexit();
 	return -1;  // not reached

src/cmd/ld/lib.h

@@ -211,31 +211,33 @@ enum {
 
 /* executable header types */
 enum {
-   Hgarbunix = 0,	// garbage unix
-   Hnoheader,		// no header
-   Hunixcoff,		// unix coff
-   Hrisc,		// aif for risc os
-   Hplan9x32,		// plan 9 32-bit format
-   Hplan9x64,		// plan 9 64-bit format
-   Hmsdoscom,		// MS-DOS .COM
-   Hnetbsd,		// NetBSD
-   Hmsdosexe,		// fake MS-DOS .EXE
-   Hixp1200,		// IXP1200 (raw)
-   Helf,		// ELF32
-   Hipaq,		// ipaq
-   Hdarwin,		// Apple Mach-O
-   Hlinux,		// Linux ELF
-   Hnacl,		// Google Native Client
-   Hfreebsd,		// FreeBSD ELF
-   Hwindows,		// MS Windows PE
-   Htiny		// tiny (os image)
+	Hgarbunix = 0,	// garbage unix
+	Hnoheader,	// no header
+	Hunixcoff,	// unix coff
+	Hrisc,		// aif for risc os
+	Hplan9x32,	// plan 9 32-bit format
+	Hplan9x64,	// plan 9 64-bit format
+	Hmsdoscom,	// MS-DOS .COM
+	Hnetbsd,	// NetBSD
+	Hmsdosexe,	// fake MS-DOS .EXE
+	Hixp1200,	// IXP1200 (raw)
+	Helf,		// ELF32
+	Hipaq,		// ipaq
+	Hdarwin,	// Apple Mach-O
+	Hlinux,		// Linux ELF
+	Hnacl,		// Google Native Client
+	Hfreebsd,	// FreeBSD ELF
+	Hwindows,	// MS Windows PE
+	Htiny		// tiny (os image)
 };
 
 typedef struct Header Header;
 struct Header {
-   char *name;
-   int val;
+	char *name;
+	int val;
 };
 
-extern Header headers[];
-int headtype(char*);
+EXTERN	char*	headstring;
+extern	Header	headers[];
+
+int	headtype(char*);

src/cmd/ld/pe.c

@@ -526,7 +526,10 @@ asmbpe(void)
 	set(MinorSubsystemVersion, 0);
 	set(SizeOfImage, nextsectoff);
 	set(SizeOfHeaders, PEFILEHEADR);
-	set(Subsystem, 3);	// WINDOWS_CUI
+	if(strcmp(headstring, "windowsgui") == 0)
+		set(Subsystem, IMAGE_SUBSYSTEM_WINDOWS_GUI);
+	else
+		set(Subsystem, IMAGE_SUBSYSTEM_WINDOWS_CUI);
 	set(SizeOfStackReserve, 0x0040000);
 	set(SizeOfStackCommit, 0x00001000);
 	set(SizeOfHeapReserve, 0x00100000);

src/cmd/ld/pe.h

@@ -131,6 +131,9 @@ enum {
 	IMAGE_DIRECTORY_ENTRY_IAT = 12,
 	IMAGE_DIRECTORY_ENTRY_DELAY_IMPORT = 13,
 	IMAGE_DIRECTORY_ENTRY_COM_DESCRIPTOR = 14,
+
+	IMAGE_SUBSYSTEM_WINDOWS_GUI = 2,
+	IMAGE_SUBSYSTEM_WINDOWS_CUI = 3,
 };
 
 void peinit(void);

src/pkg/exp/wingui/Makefile

@@ -6,6 +6,8 @@ GOOS=windows
 
 include ../../../Make.inc
 
+LD:=$(LD) -Hwindowsgui
+
 TARG=wingui
 
 GOFILES=\