video_core/host_shaders: Add support for prebuilt SPIR-V shaders

Add support for building SPIR-V shaders from GLSL and generating headers
to include the text of those same GLSL shaders to consume from OpenGL.

src/video_core/host_shaders/CMakeLists.txt

-set(SHADER_SOURCES
+set(SHADER_FILES
     opengl_present.frag
     opengl_present.vert
 )
 
+find_program(GLSLANGVALIDATOR "glslangValidator" REQUIRED)
+
+set(GLSL_FLAGS "")
+
 set(SHADER_INCLUDE ${CMAKE_CURRENT_BINARY_DIR}/include)
 set(SHADER_DIR ${SHADER_INCLUDE}/video_core/host_shaders)
 set(HOST_SHADERS_INCLUDE ${SHADER_INCLUDE} PARENT_SCOPE)
@@ -10,27 +14,44 @@ set(HOST_SHADERS_INCLUDE ${SHADER_INCLUDE} PARENT_SCOPE)
 set(INPUT_FILE ${CMAKE_CURRENT_SOURCE_DIR}/source_shader.h.in)
 set(HEADER_GENERATOR ${CMAKE_CURRENT_SOURCE_DIR}/StringShaderHeader.cmake)
 
-foreach(FILENAME IN ITEMS ${SHADER_SOURCES})
+foreach(FILENAME IN ITEMS ${SHADER_FILES})
     string(REPLACE "." "_" SHADER_NAME ${FILENAME})
     set(SOURCE_FILE ${CMAKE_CURRENT_SOURCE_DIR}/${FILENAME})
-    set(HEADER_FILE ${SHADER_DIR}/${SHADER_NAME}.h)
-    add_custom_command(
-        OUTPUT
-            ${HEADER_FILE}
-        COMMAND
-            ${CMAKE_COMMAND} -P ${HEADER_GENERATOR} ${SOURCE_FILE} ${HEADER_FILE} ${INPUT_FILE}
-        MAIN_DEPENDENCY
-            ${SOURCE_FILE}
-        DEPENDS
-            ${INPUT_FILE}
-            # HEADER_GENERATOR should be included here but msbuild seems to assume it's always modified
-    )
-    set(SHADER_HEADERS ${SHADER_HEADERS} ${HEADER_FILE})
+    # Skip generating source headers on Vulkan exclusive files
+    if (NOT ${FILENAME} MATCHES "vulkan.*")
+        set(SOURCE_HEADER_FILE ${SHADER_DIR}/${SHADER_NAME}.h)
+        add_custom_command(
+            OUTPUT
+                ${SOURCE_HEADER_FILE}
+            COMMAND
+                ${CMAKE_COMMAND} -P ${HEADER_GENERATOR} ${SOURCE_FILE} ${SOURCE_HEADER_FILE} ${INPUT_FILE}
+            MAIN_DEPENDENCY
+                ${SOURCE_FILE}
+            DEPENDS
+                ${INPUT_FILE}
+                # HEADER_GENERATOR should be included here but msbuild seems to assume it's always modified
+        )
+        set(SHADER_HEADERS ${SHADER_HEADERS} ${SOURCE_HEADER_FILE})
+    endif()
+    # Skip compiling to SPIR-V OpenGL exclusive files
+    if (NOT ${FILENAME} MATCHES "opengl.*")
+        string(TOUPPER ${SHADER_NAME}_SPV SPIRV_VARIABLE_NAME)
+        set(SPIRV_HEADER_FILE ${SHADER_DIR}/${SHADER_NAME}_spv.h)
+        add_custom_command(
+            OUTPUT
+                ${SPIRV_HEADER_FILE}
+            COMMAND
+                ${GLSLANGVALIDATOR} -V ${GLSL_FLAGS} --variable-name ${SPIRV_VARIABLE_NAME} -o ${SPIRV_HEADER_FILE} ${SOURCE_FILE}
+            MAIN_DEPENDENCY
+                ${SOURCE_FILE}
+        )
+        set(SHADER_HEADERS ${SHADER_HEADERS} ${SPIRV_HEADER_FILE})
+    endif()
 endforeach()
 
 add_custom_target(host_shaders
     DEPENDS
         ${SHADER_HEADERS}
     SOURCES
-        ${SHADER_SOURCES}
+        ${SHADER_FILES}
 )