scons: Build NIR.

Emil Velikov:
 - Attribute the src/{glsl,compiler}/nir move
 - Flesh out to separate SConscript

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
diff --git a/src/compiler/SConscript b/src/compiler/SConscript
index 8969d82..10c79c4 100644
--- a/src/compiler/SConscript
+++ b/src/compiler/SConscript
@@ -22,3 +22,4 @@
 Export('compiler')
 
 SConscript('SConscript.glsl')
+SConscript('SConscript.nir')