[ruby/fcntl] Expose Fcntl::VERSION

https://github.com/ruby/fcntl/commit/cb8e414e9f

ext/fcntl/fcntl.c

@@ -61,10 +61,16 @@ pack up your own arguments to pass as args for locking functions, etc.
  *   f.fcntl(Fcntl::F_SETFL, Fcntl::O_NONBLOCK|m)
  *
  */
+
+#define FCNTL_VERSION "1.0.2"
+
 void
 Init_fcntl(void)
 {
     VALUE mFcntl = rb_define_module("Fcntl");
+
+    rb_define_const(mFcntl, "VERSION", rb_str_new_cstr(FCNTL_VERSION));
+
 #ifdef F_DUPFD
     /* Document-const: F_DUPFD
      *

ext/fcntl/fcntl.gemspec

@@ -1,9 +1,19 @@
 # coding: utf-8
 # frozen_string_literal: true
 
+source_version = ["", "ext/fcntl/"].find do |dir|
+  begin
+    break File.open(File.join(__dir__, "#{dir}fcntl.c")) {|f|
+      f.gets("\n#define FCNTL_VERSION ")
+      f.gets[/\s*"(.+)"/, 1]
+    }
+  rescue Errno::ENOENT
+  end
+end
+
 Gem::Specification.new do |spec|
   spec.name          = "fcntl"
-  spec.version       = "1.0.2"
+  spec.version       = source_version
   spec.authors       = ["Yukihiro Matsumoto"]
   spec.email         = ["matz@ruby-lang.org"]