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This prepares for a future patch that will prefer 64-bit EMACS_INT if
available.  That patch can be tried now, by compiling with -DWIDE_EMACS_INT,
but it is temporarily not the default so that it can be further tested.

Also, install some other fixes for problems discovered by the static
checking of GCC 4.6.0.

Fixes: debbugs:8545 debbugs:8601 debbugs:8600 debbugs:8602