GPU: Make polylines vertex shader use C++ shader compilation

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Pull Request: https://projects.blender.org/blender/blender/pulls/138411

source/blender/gpu/shaders/CMakeLists.txt

@@ -20,6 +20,7 @@ set(SRC_GLSL_VERT
   gpu_shader_2D_point_uniform_size_aa_vert.glsl
   gpu_shader_2D_point_uniform_size_outline_aa_vert.glsl
   gpu_shader_2D_point_varying_size_varying_color_vert.glsl
+  gpu_shader_3D_polyline_vert.glsl
   gpu_shader_2D_vert.glsl
   gpu_shader_2D_widget_base_vert.glsl
   gpu_shader_2D_widget_shadow_vert.glsl

source/blender/gpu/shaders/gpu_shader_3D_polyline_vert.glsl

@@ -2,11 +2,15 @@
  *
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
+#include "infos/gpu_shader_3D_polyline_info.hh"
+
 #include "gpu_shader_attribute_load_lib.glsl"
 #include "gpu_shader_index_load_lib.glsl"
 #include "gpu_shader_math_base_lib.glsl"
 #include "gpu_shader_utildefines_lib.glsl"
 
+VERTEX_SHADER_CREATE_INFO(gpu_shader_3D_polyline_flat_color)
+
 struct VertIn {
   float3 ls_P;
   float4 final_color;