underscore attributes to not collide with macros

[crosdahl]

Attributes without underscores expand improperly when already defined as "language keywords"

#define noinline __attribute__((__noinline__))

// ok
noinline void f() {
        ...
}

// ok
__attribute__((__noinline__)) void g(void) {
        ...
}```

// error
__attribute__((noinline)) void h(void) {
        ...
}```

[Cyan4973]

Do you imply some of these attributes were effectively inactive before this patch ?

[crosdahl]

No, the non-underscored attribute names (e.g. noinline), clash with my usage of #define noinline __attribute__((__noinline__)). Alias attribute names with underscores exist so that you can use them even if they have been defined to something else. Currently the code depends on noinline,packed,aligned,noescape,etc not being a macro, forbidding code that uses xxhash to use those identifiers

[Cyan4973]

lgtm