shaders: Address PR review feedback.

src/video_core/engines/shader_bytecode.h

@@ -247,6 +247,7 @@ static_assert(sizeof(OpCode) == 0x8, "Incorrect structure size");
 
 namespace std {
 
+// TODO(bunne): The below is forbidden by the C++ standard, but works fine. See #330.
 template <>
 struct make_unsigned<Tegra::Shader::Attribute> {
     using type = Tegra::Shader::Attribute;
@@ -281,7 +282,6 @@ enum class SubOp : u64 {
     Rsq = 0x5,
 };
 
-#pragma pack(1)
 union Instruction {
     Instruction& operator=(const Instruction& instr) {
         hex = instr.hex;

src/video_core/renderer_opengl/gl_shader_decompiler.cpp

@@ -448,17 +448,19 @@ private:
 
         for (const auto& index : declr_input_attribute) {
             // TODO(bunnei): Use proper number of elements for these
-            declarations.AddLine(
-                "layout(location = " + std::to_string(static_cast<u32>(index) - 8) + ") in vec4 " +
-                GetInputAttribute(index) + ";");
+            declarations.AddLine("layout(location = " +
+                                 std::to_string(static_cast<u32>(index) -
+                                                static_cast<u32>(Attribute::Index::Attribute_0)) +
+                                 ") in vec4 " + GetInputAttribute(index) + ";");
         }
         declarations.AddLine("");
 
         for (const auto& index : declr_output_attribute) {
             // TODO(bunnei): Use proper number of elements for these
-            declarations.AddLine(
-                "layout(location = " + std::to_string(static_cast<u32>(index) - 8) + ") out vec4 " +
-                GetOutputAttribute(index) + ";");
+            declarations.AddLine("layout(location = " +
+                                 std::to_string(static_cast<u32>(index) -
+                                                static_cast<u32>(Attribute::Index::Attribute_0)) +
+                                 ") out vec4 " + GetOutputAttribute(index) + ";");
         }
         declarations.AddLine("");
     }