mesa: Add texcompress_rgtc.c to SConscript.
diff --git a/src/mesa/SConscript b/src/mesa/SConscript
index ea04fb1..90fec12 100644
--- a/src/mesa/SConscript
+++ b/src/mesa/SConscript
@@ -106,6 +106,7 @@
     'main/stencil.c',
     'main/syncobj.c',
     'main/texcompress.c',
+    'main/texcompress_rgtc.c',
     'main/texcompress_s3tc.c',
     'main/texcompress_fxt1.c',
     'main/texenv.c',