GraphicsPipeline: export preset data symbols from the Windows DLL

The GPU_BlendState* and GPU_GraphicsPipeline* presets are the only
exported global *data* in the library (everything else is functions or
Class descriptors). clang-cl propagates __declspec(dllexport) from a
prior declaration to a function definition, but not to a variable
definition, so these consts were compiled into ObjectivelyGPU.dll
without export records and were absent from the import library. That
broke downstream links on Windows (e.g. Quetoo's renderer):

  lld-link : error : undefined symbol: GPU_BlendStateOpaque
  lld-link : error : undefined symbol: GPU_GraphicsPipeline3D
  ...

Add an OBJECTIVELYGPU_EXPORT_DATA macro (dllexport/dllimport on the
Windows DLL build, empty elsewhere) and apply it to the preset
definitions so the symbols are exported. Using a dedicated data macro
rather than OBJECTIVELYGPU_EXPORT (which is `extern`) also avoids a
-Wextern-initializer warning on the autotools/Linux build.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jdolan

ObjectivelyGPU.vs15/Sources/WindowlyGPU.h

@@ -25,6 +25,8 @@
 
 #ifdef BUILDING_OBJECTIVELYGPU
  #define OBJECTIVELYGPU_EXPORT extern __declspec(dllexport)
+ #define OBJECTIVELYGPU_EXPORT_DATA __declspec(dllexport)
 #else
  #define OBJECTIVELYGPU_EXPORT __declspec(dllimport)
+ #define OBJECTIVELYGPU_EXPORT_DATA __declspec(dllimport)
 #endif

Sources/ObjectivelyGPU/GraphicsPipeline.c

@@ -30,11 +30,11 @@
 
 #pragma mark - Presets
 
-const SDL_GPUColorTargetBlendState GPU_BlendStateOpaque = {
+OBJECTIVELYGPU_EXPORT_DATA const SDL_GPUColorTargetBlendState GPU_BlendStateOpaque = {
   .enable_blend = false,
 };
 
-const SDL_GPUColorTargetBlendState GPU_BlendStateAlpha = {
+OBJECTIVELYGPU_EXPORT_DATA const SDL_GPUColorTargetBlendState GPU_BlendStateAlpha = {
   .enable_blend = true,
   .src_color_blendfactor = SDL_GPU_BLENDFACTOR_SRC_ALPHA,
   .dst_color_blendfactor = SDL_GPU_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
@@ -44,7 +44,7 @@ const SDL_GPUColorTargetBlendState GPU_BlendStateAlpha = {
   .alpha_blend_op = SDL_GPU_BLENDOP_ADD,
 };
 
-const SDL_GPUColorTargetBlendState GPU_BlendStatePremultipliedAlpha = {
+OBJECTIVELYGPU_EXPORT_DATA const SDL_GPUColorTargetBlendState GPU_BlendStatePremultipliedAlpha = {
   .enable_blend = true,
   .src_color_blendfactor = SDL_GPU_BLENDFACTOR_ONE,
   .dst_color_blendfactor = SDL_GPU_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
@@ -54,7 +54,7 @@ const SDL_GPUColorTargetBlendState GPU_BlendStatePremultipliedAlpha = {
   .alpha_blend_op = SDL_GPU_BLENDOP_ADD,
 };
 
-const SDL_GPUColorTargetBlendState GPU_BlendStateAdditive = {
+OBJECTIVELYGPU_EXPORT_DATA const SDL_GPUColorTargetBlendState GPU_BlendStateAdditive = {
   .enable_blend = true,
   .src_color_blendfactor = SDL_GPU_BLENDFACTOR_SRC_ALPHA,
   .dst_color_blendfactor = SDL_GPU_BLENDFACTOR_ONE,
@@ -64,7 +64,7 @@ const SDL_GPUColorTargetBlendState GPU_BlendStateAdditive = {
   .alpha_blend_op = SDL_GPU_BLENDOP_ADD,
 };
 
-const SDL_GPUGraphicsPipelineCreateInfo GPU_GraphicsPipeline3D = {
+OBJECTIVELYGPU_EXPORT_DATA const SDL_GPUGraphicsPipelineCreateInfo GPU_GraphicsPipeline3D = {
   .primitive_type = SDL_GPU_PRIMITIVETYPE_TRIANGLELIST,
   .rasterizer_state = {
     .fill_mode = SDL_GPU_FILLMODE_FILL,
@@ -82,7 +82,7 @@ const SDL_GPUGraphicsPipelineCreateInfo GPU_GraphicsPipeline3D = {
   },
 };
 
-const SDL_GPUGraphicsPipelineCreateInfo GPU_GraphicsPipeline2D = {
+OBJECTIVELYGPU_EXPORT_DATA const SDL_GPUGraphicsPipelineCreateInfo GPU_GraphicsPipeline2D = {
   .primitive_type = SDL_GPU_PRIMITIVETYPE_TRIANGLELIST,
   .rasterizer_state = {
     .fill_mode = SDL_GPU_FILLMODE_FILL,

Sources/ObjectivelyGPU/Types.h

@@ -35,6 +35,10 @@
  #define OBJECTIVELYGPU_EXPORT extern
 #endif
 
+#ifndef OBJECTIVELYGPU_EXPORT_DATA
+ #define OBJECTIVELYGPU_EXPORT_DATA
+#endif
+
 typedef struct SDL_Size SDL_Size;
 
 /**