LibGL: Stub glStencilMask

Xash3D requires this otherwise it will crash with a jump to nullptr,
but it doesn't use it for anything interesting and just sets a default
value of ~0 during initialization.

Userland/Libraries/LibGL/GL/gl.h

@@ -584,6 +584,7 @@ GLAPI void glStencilFunc(GLenum func, GLint ref, GLuint mask);
 GLAPI void glStencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask);
 GLAPI void glStencilOp(GLenum sfail, GLenum dpfail, GLenum dppass);
 GLAPI void glStencilOpSeparate(GLenum face, GLenum sfail, GLenum dpfail, GLenum dppass);
+GLAPI void glStencilMask(GLuint mask);
 GLAPI void glNormal3f(GLfloat nx, GLfloat ny, GLfloat nz);
 GLAPI void glNormal3fv(GLfloat const* v);
 GLAPI void glNormalPointer(GLenum type, GLsizei stride, void const* pointer);

Userland/Libraries/LibGL/GLStencil.cpp

@@ -33,3 +33,8 @@ void glStencilOpSeparate(GLenum face, GLenum sfail, GLenum dpfail, GLenum dppass
 {
     g_gl_context->gl_stencil_op_separate(face, sfail, dpfail, dppass);
 }
+
+void glStencilMask(GLuint mask)
+{
+    dbgln("(STUBBED) glStencilMask(0x{:08x})", mask);
+}