i965: Call spirv_to_nir() instead of glsl_to_nir() for SPIR-V shaders

This is the main fork of the shader compilation code-path, where a NIR
shader is obtained by calling spirv_to_nir() or glsl_to_nir(),
depending on its nature..

v2: Use 'spirv_data' member from gl_linked_shader to know which method
   to call. (Timothy Arceri)

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/mesa/drivers/dri/i965/brw_program.c

@@ -31,6 +31,7 @@
 
 #include <pthread.h>
 #include "main/imports.h"
+#include "main/glspirv.h"
 #include "program/prog_parameter.h"
 #include "program/prog_print.h"
 #include "program/prog_to_nir.h"
@@ -74,9 +75,14 @@ brw_create_nir(struct brw_context *brw,
       ctx->Const.ShaderCompilerOptions[stage].NirOptions;
    nir_shader *nir;
 
-   /* First, lower the GLSL IR or Mesa IR to NIR */
+   /* First, lower the GLSL/Mesa IR or SPIR-V to NIR */
    if (shader_prog) {
-      nir = glsl_to_nir(shader_prog, stage, options);
+      if (shader_prog->_LinkedShaders[stage]->spirv_data)
+         nir = _mesa_spirv_to_nir(ctx, shader_prog, stage, options);
+      else
+         nir = glsl_to_nir(shader_prog, stage, options);
+      assert (nir);
+
       nir_remove_dead_variables(nir, nir_var_shader_in | nir_var_shader_out);
       nir_lower_returns(nir);
       nir_validate_shader(nir);