glsl: Add standalone_scaffolding.cpp to SConscript.
diff --git a/src/glsl/SConscript b/src/glsl/SConscript
index ea104ab..1da58a9 100644
--- a/src/glsl/SConscript
+++ b/src/glsl/SConscript
@@ -96,6 +96,7 @@
     'opt_tree_grafting.cpp',
     'ralloc.c',
     's_expression.cpp',
+    'standalone_scaffolding.cpp',
     'strtod.c',
 ]