Pretty print async block without redundant space

[dtolnay]

Repro:

macro_rules! m {
    ($e:expr) => { stringify!($e) };
}
fn main() {
    println!("{:?}", m!(async {}));
}

Before: "async  {}"
After: "async {}"

In this function:

rust/compiler/rustc_ast_pretty/src/pprust/state.rs

Lines 2049 to 2051 in 65c55bf

	self.word_nbsp("async");
	self.print_capture_clause(capture_clause);
	self.s.space();

the print_capture_clause and word_nbsp/word_space calls already put a space after the async and move keywords being printed. The extra self.s.space() call removed by this PR resulted in the redundant double space.

rust/compiler/rustc_ast_pretty/src/pprust/state.rs

Lines 2640 to 2645 in 65c55bf

	crate fn print_capture_clause(&mut self, capture_clause: ast::CaptureBy) {
	match capture_clause {
	ast::CaptureBy::Value => self.word_space("move"),
	ast::CaptureBy::Ref => {}
	}
	}

rust/compiler/rustc_ast_pretty/src/helpers.rs

Lines 34 to 37 in 65c55bf

	pub fn word_nbsp<S: Into<Cow<'static, str>>>(&mut self, w: S) {
	self.word(w);
	self.nbsp()
	}

rust/compiler/rustc_ast_pretty/src/helpers.rs

Lines 5 to 8 in 65c55bf

	pub fn word_space<W: Into<Cow<'static, str>>>(&mut self, w: W) {
	self.word(w);
	self.space();
	}

[rust-highfive]

r? @Mark-Simulacrum

(rust-highfive has picked a reviewer for you, use r? to override)

[Mark-Simulacrum]

@bors r+ rollup

[bors]

📌 Commit 33c29a3 has been approved by Mark-Simulacrum