automake,scons: Put NIR source files in a separate var to fix SCons build.

SCons does not build NIR yet.

Trivial.

src/gallium/auxiliary/Makefile.am

@@ -22,6 +22,7 @@ AM_CXXFLAGS = \
 
 libgallium_la_SOURCES = \
 	$(C_SOURCES) \
+	$(NIR_SOURCES) \
 	$(GENERATED_SOURCES)
 
 if HAVE_MESA_LLVM

src/gallium/auxiliary/Makefile.sources

@@ -69,7 +69,6 @@ C_SOURCES := \
 	indices/u_indices_priv.h \
 	indices/u_primconvert.c \
 	indices/u_primconvert.h \
-	nir/tgsi_to_nir.c \
 	os/os_memory_aligned.h \
 	os/os_memory_debug.h \
 	os/os_memory_stdc.h \
@@ -303,6 +302,9 @@ C_SOURCES := \
 	util/u_vbuf.h \
 	util/u_video.h
 
+NIR_SOURCES := \
+	nir/tgsi_to_nir.c
+
 VL_SOURCES := \
 	vl/vl_compositor.c \
 	vl/vl_compositor.h \