cmd/dist: fix superfluous and confusing "binaries ... to be copied or moved" message

Also, to aid debugging cmd/dist, make make.bat support --dist-tool flag.

Fixes #3100.

R=alex.brainman
CC=golang-dev
https://golang.org/cl/6637061

src/cmd/dist/a.h

@@ -150,3 +150,4 @@ int	xstrlen(char*);
 char*	xstrrchr(char*, int);
 char*	xstrstr(char*, char*);
 char*	xworkdir(void);
+int	xsamefile(char*, char*);

src/cmd/dist/build.c

@@ -1564,7 +1564,7 @@ cmdbanner(int argc, char **argv)
 				"Read and run ./sudo.bash to install the debuggers.\n");
 	}
 
-	if(!streq(goroot_final, goroot)) {
+	if(!xsamefile(goroot_final, goroot)) {
 		xprintf("\n"
 			"The binaries expect %s to be copied or moved to %s\n",
 			goroot, goroot_final);

src/cmd/dist/plan9.c

@@ -742,4 +742,11 @@ xstrrchr(char *p, int c)
 	return strrchr(p, c);
 }
 
+// xsamefile returns whether f1 and f2 are the same file (or dir)
+int
+xsamefile(char *f1, char *f2)
+{
+	return streq(f1, f2); // suffice for now
+}
+
 #endif // PLAN9

src/cmd/dist/unix.c

@@ -727,5 +727,12 @@ xstrrchr(char *p, int c)
 	return strrchr(p, c);
 }
 
+// xsamefile returns whether f1 and f2 are the same file (or dir)
+int
+xsamefile(char *f1, char *f2)
+{
+	return streq(f1, f2); // suffice for now
+}
+
 #endif // PLAN9
 #endif // __WINDOWS__

src/cmd/dist/windows.c

@@ -925,4 +925,41 @@ xstrrchr(char *p, int c)
 	return nil;
 }
 
+// xsamefile returns whether f1 and f2 are the same file (or dir)
+int
+xsamefile(char *f1, char *f2)
+{
+	Rune *ru;
+	HANDLE fd1, fd2;
+	BY_HANDLE_FILE_INFORMATION fi1, fi2;
+	int r;
+
+	// trivial case
+	if(streq(f1, f2))
+		return 1;
+	
+	torune(&ru, f1);
+	// refer to ../../pkg/os/stat_windows.go:/sameFile
+	fd1 = CreateFileW(ru, 0, 0, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0);
+	xfree(ru);
+	if(fd1 == INVALID_HANDLE_VALUE)
+		return 0;
+	torune(&ru, f2);
+	fd2 = CreateFileW(ru, 0, 0, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, 0);
+	xfree(ru);
+	if(fd2 == INVALID_HANDLE_VALUE) {
+		CloseHandle(fd1);
+		return 0;
+	}
+	r = GetFileInformationByHandle(fd1, &fi1) != 0 && GetFileInformationByHandle(fd2, &fi2) != 0;
+	CloseHandle(fd2);
+	CloseHandle(fd1);
+	if(r != 0 &&
+	   fi1.dwVolumeSerialNumber == fi2.dwVolumeSerialNumber &&
+	   fi1.nFileIndexHigh == fi2.nFileIndexHigh &&
+	   fi1.nFileIndexLow == fi2.nFileIndexLow)
+	   	return 1;
+	return 0;
+}
+
 #endif // __WINDOWS__

src/make.bat

@@ -68,6 +68,9 @@ call env.bat
 del env.bat
 echo.
 
+if x%1==x--dist-tool goto copydist
+if x%2==x--dist-tool goto copydist
+
 echo # Building compilers and Go bootstrap tool.
 set buildall=-a
 if x%1==x--no-clean set buildall=
@@ -105,6 +108,11 @@ if x%1==x--no-banner goto nobanner
 
 goto end
 
+:copydist
+mkdir %GOTOOLDIR% 2>NUL
+copy cmd\dist\dist.exe %GOTOOLDIR%\
+goto end
+
 :fail
 set GOBUILDFAIL=1