MFC r289837

resolver: abuse _res a little less

In the past, _res was a global variable. Now, it's multiple function calls.
Several functions in the resolver use _res multiple times and therefore
call the function(s) far more than necessary.

Fix those callers to store the result of _res in a local variable.

Add __noinline to the definition of res_init() to avoid the code bloat
that these changes would have otherwise incurred. Thanks to jilles
for noticing this.

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