VsCode - Intellisense complaining about incorrect macro definitions

Modified OpenColor header to check if GNUC is defined before using it (as it already does a few lines below). And thus removed the global invalid GNUC define which confuses VsCode.

Fixed up spaces in define that also confused VsCode.

#rb simon.therriault
[fyi] ben.marsh

#jira UE-76985
(ushell-p4-cherrypick of 7288701 by Joakim.Lindqvist)

#ROBOMERGE-SOURCE: CL 7865169 in //UE4/Release-4.23/...
#ROBOMERGE-BOT: RELEASE (Release-4.23 -> Main) (v389-7813075)

[CL 7865209 by joakim lindqvist in Main branch]

Engine/Source/Programs/UnrealBuildTool/ProjectFiles/VisualStudioCode/VSCodeProjectFileGenerator.cs

@@ -440,6 +440,8 @@ namespace UnrealBuildTool
 					foreach (string Definition in Project.IntelliSensePreprocessorDefinitions)
 					{
 						string Processed = Definition.Replace("\"", "\\\"");
+						// removing trailing spaces on preprocessor definitions as these can be added as empty defines confusing vscode
+						Processed = Processed.TrimEnd(' ');
 						if (!ProjectData.CombinedPreprocessorDefinitions.Contains(Processed))
 						{
 							ProjectData.CombinedPreprocessorDefinitions.Add(Processed);