GLSL: Handle empty block declarations.

Similar fix as for structs.

reference/shaders-no-opt/asm/comp/empty-ubo-block.noeliminate.asm.comp

@@ -0,0 +1,12 @@
+#version 460
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+
+layout(binding = 15, std140) uniform type_Primitive
+{
+    int empty_struct_member;
+} Primitive;
+
+void main()
+{
+}
+

shaders-no-opt/asm/comp/empty-ubo-block.noeliminate.asm.comp

@@ -0,0 +1,21 @@
+               OpCapability Shader
+          %1 = OpExtInstImport "GLSL.std.450"
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint GLCompute %main "main"
+               OpExecutionMode %main LocalSize 1 1 1
+               OpSource GLSL 460
+               OpName %main "main"
+               OpName %type_Primitive "type_Primitive"
+               OpName %Primitive "Primitive"
+               OpDecorate %type_Primitive Block
+               OpDecorate %Primitive DescriptorSet 0
+               OpDecorate %Primitive Binding 15
+       %void = OpTypeVoid
+          %3 = OpTypeFunction %void
+%type_Primitive = OpTypeStruct
+%_ptr_Uniform_type_Primitive = OpTypePointer Uniform %type_Primitive
+  %Primitive = OpVariable %_ptr_Uniform_type_Primitive Uniform
+       %main = OpFunction %void None %3
+          %5 = OpLabel
+               OpReturn
+               OpFunctionEnd

spirv_glsl.cpp

@@ -2465,6 +2465,10 @@ void CompilerGLSL::emit_buffer_block_native(const SPIRVariable &var)
 		i++;
 	}
 
+	// Don't declare empty blocks in GLSL, this is not allowed.
+	if (type_is_empty(type) && !backend.supports_empty_struct)
+		statement("int empty_struct_member;");
+
 	// var.self can be used as a backup name for the block name,
 	// so we need to make sure we don't disturb the name here on a recompile.
 	// It will need to be reset if we have to recompile.