scripts/nsis.py: Fix destination directory name when invoked on Windows

"make installer" on Windows fails with the following message:

  Traceback (most recent call last):
    File "G:\msys64\home\foo\git\qemu\scripts\nsis.py", line 89, in <module>
      main()
    File "G:\msys64\home\foo\git\qemu\scripts\nsis.py", line 34, in main
      with open(
  OSError: [Errno 22] Invalid argument:
  'R:/Temp/tmpw83xhjquG:/msys64/qemu/system-emulations.nsh'
  ninja: build stopped: subcommand failed.

Use os.path.splitdrive() to form a canonical path without the drive
letter on Windows. This works with cross-build on Linux too.

Fixes: 8adfeba953e0 ("meson: add NSIS building")
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Message-Id: <20220908132817.1831008-3-bmeng.cn@gmail.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Stefan Weil <sw@weilnetz.de>

scripts/nsis.py

@@ -28,16 +28,18 @@ def main():
     parser.add_argument("nsisargs", nargs="*")
     args = parser.parse_args()
 
+    # canonicalize the Windows native prefix path
+    prefix = os.path.splitdrive(args.prefix)[1]
     destdir = tempfile.mkdtemp()
     try:
         subprocess.run(["make", "install", "DESTDIR=" + destdir])
         with open(
-            os.path.join(destdir + args.prefix, "system-emulations.nsh"), "w"
+            os.path.join(destdir + prefix, "system-emulations.nsh"), "w"
         ) as nsh, open(
-            os.path.join(destdir + args.prefix, "system-mui-text.nsh"), "w"
+            os.path.join(destdir + prefix, "system-mui-text.nsh"), "w"
         ) as muinsh:
             for exe in sorted(glob.glob(
-                os.path.join(destdir + args.prefix, "qemu-system-*.exe")
+                os.path.join(destdir + prefix, "qemu-system-*.exe")
             )):
                 exe = os.path.basename(exe)
                 arch = exe[12:-4]
@@ -61,7 +63,7 @@ def main():
                 !insertmacro MUI_DESCRIPTION_TEXT ${{Section_{0}}} "{1}"
                 """.format(arch, desc))
 
-        for exe in glob.glob(os.path.join(destdir + args.prefix, "*.exe")):
+        for exe in glob.glob(os.path.join(destdir + prefix, "*.exe")):
             signcode(exe)
 
         makensis = [
@@ -69,7 +71,7 @@ def main():
             "-V2",
             "-NOCD",
             "-DSRCDIR=" + args.srcdir,
-            "-DBINDIR=" + destdir + args.prefix,
+            "-DBINDIR=" + destdir + prefix,
         ]
         dlldir = "w32"
         if args.cpu == "x86_64":