configure: Warn for a 64-bit build without CFI directive support.

[Ken Thomases]

On 64-bit, DWARF unwind info is crucial for unwinding the stack during
exception handling.  Without support for CFI directives, Wine's assembly code
won't have DWARF unwind info and stack unwinding will go badly wrong.

This means, for example, that RtlRaiseException won't be able to unwind out of
itself.
---
configure.ac | 4 ++++
1 file changed, 4 insertions(+)

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