The dirty-skip commit staged the header via a lowercase path (l4vb16.h) while git
tracks it as L4VB16.h on this case-insensitive FS, so the PlaneChecksum declaration
was left out -- c9e25e5 as committed would not build from clean (L4VB16.cpp defines
SVGA16::PlaneChecksum, L4GLASSWIN.cpp calls it, but the header never declared it).
This adds the one-line decl. HEAD now builds standalone.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>