nsis: Add QEMU version information to Windows registry

The uninstall keys include an option key "DisplayVersion" which we set
now. By default the version value is read from file VERSION, but it is
also possible to pass VERSION=#.#.# to make.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
diff --git a/qemu.nsi b/qemu.nsi
index cc5fafd..a20f6ef 100644
--- a/qemu.nsi
+++ b/qemu.nsi
@@ -139,6 +139,9 @@
 
     ; Write the uninstall keys for Windows
     WriteRegStr HKLM "${UNINST_KEY}" "DisplayName" "QEMU"
+!ifdef DISPLAYVERSION
+    WriteRegStr HKLM "${UNINST_KEY}" "DisplayVersion" "${DISPLAYVERSION}"
+!endif
     WriteRegStr HKLM "${UNINST_KEY}" "UninstallString" '"${UNINST_EXE}"'
     WriteRegDWORD HKLM "${UNINST_KEY}" "NoModify" 1
     WriteRegDWORD HKLM "${UNINST_KEY}" "NoRepair" 1