Prevent empty "ungroupable" enums from being output and fix EnumGroupRegression test case (#2525)

This fixes the Constants_* and enums_* groups from being output for the OpenCL XML spec in the EnumGroupRegression test case.
The change to cl_compiler_mode_altera is justifiable since it is an empty enum.

Author: Exanite

sources/SilkTouch/SilkTouch/Mods/MixKhronosData.cs

@@ -2278,7 +2278,7 @@ var group in (groupName is null ? Enumerable.Empty<string>() : [groupName])
             }
 
             // Some enum groups don't have members, meaning that the code above won't catch them
-            if (groupName != null && !data.Groups.ContainsKey(groupName))
+            if (groupName != null && !IsUngroupable(groupName) && !data.Groups.ContainsKey(groupName))
             {
                 data.Groups[groupName] = new EnumGroup(
                     groupName,

tests/SilkTouch/SilkTouch/Khronos/MixKhronosDataTests.EnumGroupRegression.cl.xml.verified.txt

@@ -15,6 +15,8 @@ Added Group: cl_arm_svm_alloc_flags
 Existing Group: cl_command_queue_properties
     Added: CL_QUEUE_RESERVED_QCOM
 
+Added Group: cl_compiler_mode_altera
+
 Added Group: cl_device_command_buffer_capabilities_khr 
     Added: CL_COMMAND_BUFFER_CAPABILITY_DEVICE_SIDE_ENQUEUE_KHR
     Added: CL_COMMAND_BUFFER_CAPABILITY_KERNEL_PRINTF_KHR