compiler: Move glsl_to_nir to libglsl.la

Right now libglsl.la depends on libnir.la so putting it in libnir.la
adds a dependency on libglsl.la that goes the wrong direction.

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
diff --git a/src/compiler/SConscript.glsl b/src/compiler/SConscript.glsl
index 474df11..4252ce1 100644
--- a/src/compiler/SConscript.glsl
+++ b/src/compiler/SConscript.glsl
@@ -17,12 +17,15 @@
     '#src/gallium/auxiliary',
     '#src/compiler/glsl',
     '#src/compiler/glsl/glcpp',
+    '#src/compiler/nir',
 ])
 
 env.Prepend(LIBS = [mesautil])
 
 # Make glcpp-parse.h and glsl_parser.h reachable from the include path.
 env.Prepend(CPPPATH = [Dir('.').abspath, Dir('glsl').abspath])
+# Make NIR headers reachable from the include path.
+env.Prepend(CPPPATH = [Dir('.').abspath, Dir('nir').abspath])
 
 glcpp_env = env.Clone()
 glcpp_env.Append(YACCFLAGS = [