In code such as:

#if SOME_MACRO(x)
#elif ANOTHER_MACRO(y)
#endif

is ANOTHER_MACRO expanded and evaluated for C++ correctness even when
the result of SOME_MACRO's expansion is 1.

I had always thought that ANOTHER_MACRO(y) could be anything, even
incorrect C++, as long as SOME_MACRO(x) is 1. But gcc always evaluates
ANOTHER_MACRO(y) and, if it is invalid C++, gives a compiler error, even
when SOME_MACRO(x) expands to 1.


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