An invalid preprocessor expression is reported as a pair of
warnings with the second giving a more detailed message from the
expression evaluator. Previously SWIG prefixed the second message
with "Error:" - that was confusing as it's actually only a warning
by default so we've now dropped this prefix.
Before:
x.i:1: Warning 202: Could not evaluate expression '1.2'
x.i:1: Warning 202: Error: 'Floating point constant in preprocessor expression'
Now:
x.i:1: Warning 202: Could not evaluate expression '1.2'
x.i:1: Warning 202: Floating point constant in preprocessor expression
See #1465
