[ruby/win32ole] Reuse WIN32OLE_VERSION for gem version

https://github.com/ruby/win32ole/commit/bff3ea8b0b

ext/win32ole/win32ole.c

@@ -27,7 +27,7 @@
 const IID IID_IMultiLanguage2 = {0xDCCFC164, 0x2B38, 0x11d2, {0xB7, 0xEC, 0x00, 0xC0, 0x4F, 0x8F, 0x5D, 0x9A}};
 #endif
 
-#define WIN32OLE_VERSION "1.8.8"
+#define WIN32OLE_VERSION "1.8.9"
 
 typedef HRESULT (STDAPICALLTYPE FNCOCREATEINSTANCEEX)
     (REFCLSID, IUnknown*, DWORD, COSERVERINFO*, DWORD, MULTI_QI*);

ext/win32ole/win32ole.gemspec

@@ -1,6 +1,16 @@
+source_version = ["", "ext/win32ole/"].find do |dir|
+  begin
+    break File.open(File.join(__dir__, "#{dir}win32ole.c")) {|f|
+      f.gets("\n#define WIN32OLE_VERSION ")
+      f.gets[/\s*"(.+)"/, 1]
+    }
+  rescue Errno::ENOENT
+  end
+end
+
 Gem::Specification.new do |spec|
   spec.name          = "win32ole"
-  spec.version       = "1.8.9"
+  spec.version       = source_version
   spec.authors       = ["Masaki Suketa"]
   spec.email         = ["suke@ruby-lang.org"]