Remove some erroneously added brackets_increment() calls.
Reject <=> in preprocessor expressions with a clear error message (it
seems it isn't supported here - clang and gcc don't at least).
The type returned by `<=>` is not `bool`. We pretend it's
`int` for now, which should work for how it's likely to be used
in constant expressions.
Fixes#1622
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
