VERSION: rename to MPV_VERSION to avoid standard library header conflict

Root directory is added to include directories and `VERSION` conflicts
with `#include <version>` which is standard library header.

DOCS/release-policy.md

@@ -24,7 +24,7 @@ While on master:
 
 - Update the `RELEASE_NOTES` file, replacing the previous release notes.
 
-- Update the `VERSION` file.
+- Update the `MPV_VERSION` file.
 
 - Update `DOCS/client-api-changes.rst` (in particular, update the last version
   number if necessary)
@@ -43,7 +43,7 @@ While on master:
 - Create a new GitHub release using the content of `RELEASE_NOTES` related to
   the new version.
 
-- Readd -UNKNOWN suffix to version in `VERSION` file.
+- Readd -UNKNOWN suffix to version in `MPV_VERSION` file.
 
 If necessary (to e.g. exclude commits already on master), the release can
 be done on a branch with different commit history. The release branch **must**

TOOLS/osxbundle.py

@@ -47,7 +47,7 @@ def sign_bundle(binary_name):
 
 def bundle_version(src_path):
     version = 'UNKNOWN'
-    version_path = os.path.join(src_path, 'VERSION')
+    version_path = os.path.join(src_path, 'MPV_VERSION')
     if os.path.exists(version_path):
         x = open(version_path)
         version = x.read()

meson.build

@@ -1,7 +1,7 @@
 project('mpv',
         'c',
         license: ['GPL2+', 'LGPL2.1+'],
-        version: files('./VERSION'),
+        version: files('./MPV_VERSION'),
         meson_version: '>=0.62.0',
         default_options: [
             'backend_max_links=16',