Bug 451091 - Make type of constexpr variable const-qualified

Change-Id: I2744ba8dbf2b629659f778d257b1d22483eb6c33
Signed-off-by: Nathan Ridge <zeratul976@hotmail.com>
Reviewed-on: https://git.eclipse.org/r/37929
Reviewed-by: Sergey Prigogin <eclipse.sprigogin@gmail.com>
Tested-by: Sergey Prigogin <eclipse.sprigogin@gmail.com>