Add missing GLU_TESS_BOUNDARY_ONLY constant for idftools

The idftools/vrml_layer.cpp uses this GLU tessellation constant
which was missing from our WASM GLU stub header.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

wasm/stubs/GL/glu.h

@@ -40,6 +40,7 @@ typedef struct GLUquadric GLUquadric;
 #define GLU_TESS_WINDING_POSITIVE   100132
 #define GLU_TESS_WINDING_NEGATIVE   100133
 #define GLU_TESS_WINDING_ABS_GEQ_TWO 100134
+#define GLU_TESS_BOUNDARY_ONLY      100141
 
 // Tesselator functions
 GLUtesselator* gluNewTess(void);