[Cmake] Ignoring temporary files in AUX_SOURCE

[Amitha Perera]

I wrote:
> I will implement this and name the commands SourceRegularExpression
> and HeaderRegularExpression. (Or is SourceFileRegularExpression
> better?)

After futher consideration, it will be easier to specify a list of
extensions instead of a full regular expression:
  SOURCE_FILE_EXTENSIONS( cxx txx cpp c )
Does anyone forsee the need for a full regular expression capability?

The issue with regular expressions in this context is that given, for
example "abc" and "^.+\.(cxx|txx)", we must determine if a file exists
that matches abc\.(cxx|txx). This implies a directory scan. Of course,
we do not want such a scan per SourceFile::SetName call, but we could
limit it to a scan per SOURCE_FILE command. Any suggestions on a
solution or workaround for this?

Thanks,
Amitha.