[gegl] build: fix lua build on msys2/mingw - msys2/mingw does not like symlinked source files so create cop

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 71b2cfa8c52db3a6dfb13980114b7c2536302e56
Author: John Marshall <jtm home gmail com>
Date:   Tue Feb 9 11:18:03 2021 +0000

    build: fix lua build on msys2/mingw
    - msys2/mingw does not like symlinked source files so create copies

 bin/lua/meson.build | 25 ++++++++++++++++++++++---
 bin/meson.build     |  3 ++-
 2 files changed, 24 insertions(+), 4 deletions(-)
---
diff --git a/bin/lua/meson.build b/bin/lua/meson.build
index 8f067f1cb..38dc98e91 100644
--- a/bin/lua/meson.build
+++ b/bin/lua/meson.build
@@ -1,15 +1,13 @@
+
 lua_files = files(
   'cairo_h.lua',
   'cairo.lua',
   'gegl_box-blur.lua',
   'gegl_c2g.lua',
-  'gegl_crop.lua',
   'gegl_edge-neon.lua',
-  'gegl_fill-path.lua',
   'gegl_gaussian-blur.lua',
   'gegl_linear-gradient.lua',
   'gegl_median-blur.lua',
-  'gegl_radial-gradient.lua',
   'gegl_rectangle.lua',
   'gegl_rotate.lua',
   'gegl_snn-mean.lua',
@@ -25,6 +23,27 @@ lua_files = files(
   'viewer.lua',
 )
 
+lua_symlink_files = {
+  'gegl_crop.lua' : 'gegl_rectangle.lua',
+  'gegl_fill-path.lua' : 'gegl_vector-stroke.lua',
+  'gegl_radial-gradient.lua' : 'gegl_linear-gradient.lua',
+}
+# Windows doesn't like *nix symlinks so we check if the symlinked lua
+# files are valid and if not copy the original to the build dir in place
+# of the symlink 
+fs=import('fs')
+foreach _link, _file : lua_symlink_files
+  if fs.is_symlink(_link)
+    lua_files += _link
+  else
+    lua_files += configure_file(
+      input: _file,
+      output: _link,
+      copy: true,
+    )
+  endif
+endforeach
+
 if lua.found()
   install_data(
     lua_files,
diff --git a/bin/meson.build b/bin/meson.build
index 4daf6cb49..36e58f377 100644
--- a/bin/meson.build
+++ b/bin/meson.build
@@ -1,4 +1,5 @@
-subdir('lua')
+
+subdir('lua', if_found: lua)
 
 gegl_sources = files(
   'gegl-options.c',