graphics/mesa-devel: fix warning with --auto-features=enabled

Run-time dependency directx-headers found: NO (tried pkgconfig and cmake)
Run-time dependency directx-headers found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency DirectX-Headers
Git program not found, cannot download DirectX-Headers.wrap via git.
Subproject DirectX-Headers is buildable: NO (disabling)
Dependency DirectX-Headers from subproject DirectX-Headers found: NO (subproject failed to configure)
[...]

Subprojects
  DirectX-Headers     : NO
                        Git program not found, cannot download DirectX-Headers.wrap via git.

PR: 270361