Fixed some of the remaining clippy warnings that needed slightly more complex refactors.

[kkysen]

I fixed some of the remaining clippy warnings (from #460) that needed slightly more complex refactors, which I want to have reviewed to make sure they're semantics-preserving.

[kkysen]

There are also 2 remaining clippy warnings that I had questions about:

• clippy::duplicate_underscore_argument:

c2rust/analysis/runtime/src/handlers.rs

Lines 15 to 21 in 2113c3e

	pub fn free(mir_loc: MirLocId, ptr: usize, _ptr: ()) {
	TX.send(Event {
	mir_loc,
	kind: EventKind::Free { ptr },
	})
	.unwrap();
	}

warning: `ptr` already exists, having another argument having almost the same name makes code comprehension and documentation more difficult
  --> analysis/runtime/src/handlers.rs:15:32
   |
15 | pub fn free(mir_loc: MirLocId, ptr: usize, _ptr: ()) {
   |                                ^^^
   |
   = note: `#[warn(clippy::duplicate_underscore_argument)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#duplicate_underscore_argument

@rinon, do you know why there are 2 ptr arguments are why the second one is ignored and has a () type? What is it there for and why is it named ptr, too?

• clippy::if_same_then_else:

c2rust/c2rust-transpile/src/translator/mod.rs

Lines 2374 to 2388 in 2113c3e

	// Only add linkage attributes if the function is `extern`
	let mut mk_ = if is_main {
	mk()
	} else if is_global && !is_inline {
	mk_linkage(false, new_name, name).extern_("C").pub_()
	} else if is_inline && is_extern && !attrs.contains(&c_ast::Attribute::GnuInline) {
	// c99 extern inline functions should be pub, but not gnu_inline attributed
	// extern inlines, which become subject to their gnu89 visibility (private)
	mk_linkage(false, new_name, name).extern_("C").pub_()
	} else if self.cur_file.borrow().is_some() {
	mk().extern_("C").pub_()
	} else {
	mk().extern_("C")
	};

error: this `if` has identical blocks
    --> c2rust-transpile/src/translator/mod.rs:2377:51
     |
2377 |                   } else if is_global && !is_inline {
     |  ___________________________________________________^
2378 | |                     mk_linkage(false, new_name, name).extern_("C").pub_()
2379 | |                 } else if is_inline && is_extern && !attrs.contains(&c_ast::Attribute::GnuInline) {
     | |_________________^
     |
     = note: `#[deny(clippy::if_same_then_else)]` on by default
note: same as this
    --> c2rust-transpile/src/translator/mod.rs:2379:99
     |
2379 |                   } else if is_inline && is_extern && !attrs.contains(&c_ast::Attribute::GnuInline) {
     |  ___________________________________________________________________________________________________^
2380 | |                     // c99 extern inline functions should be pub, but not gnu_inline attributed
2381 | |                     // extern inlines, which become subject to their gnu89 visibility (private)
2382 | |
2383 | |                     mk_linkage(false, new_name, name).extern_("C").pub_()
2384 | |                 } else if self.cur_file.borrow().is_some() {
     | |_________________^
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_same_then_else

@rinon, do you know if these two branches are meant to be identical, and if so, can they just be merged into one? I wasn't sure if they were supposed to remain separate, especially with a comment that's different in one branch.