Android: Fix build issue without LLVM

Some of the latest changes are causing the following build error on Android:

```
external/mesa3d/src/gallium/auxiliary/nir/nir_to_tgsi_info.c:403:6:
error: redefinition of 'nir_tgsi_scan_shader'
void nir_tgsi_scan_shader(const struct nir_shader *nir,
     ^
external/mesa3d/src/gallium/auxiliary/nir/nir_to_tgsi_info.h:37:20:
note: previous definition is here
static inline void nir_tgsi_scan_shader(const struct nir_shader *nir,
                   ^
```

Include nir_to_tgsi_info.c and nir_to_tgsi_info.h into the build
only if LLVM is enabled.

Signed-off-by: Roman Stratiienko <roman.stratiienko@globallogic.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2978>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2978>

src/gallium/auxiliary/Makefile.sources

@@ -318,8 +318,6 @@ C_SOURCES := \
 NIR_SOURCES := \
 	nir/tgsi_to_nir.c \
 	nir/tgsi_to_nir.h \
-	nir/nir_to_tgsi_info.c \
-	nir/nir_to_tgsi_info.h \
 	nir/nir_draw_helpers.c \
 	nir/nir_draw_helpers.h
 
@@ -451,6 +449,8 @@ GALLIVM_SOURCES := \
 	gallivm/lp_bld_tgsi_soa.c \
 	gallivm/lp_bld_type.c \
 	gallivm/lp_bld_type.h \
+	nir/nir_to_tgsi_info.c \
+	nir/nir_to_tgsi_info.h \
 	draw/draw_llvm.c \
 	draw/draw_llvm.h \
 	draw/draw_llvm_sample.c \