Auto merge of #52767 - ljedrz:avoid_format, r=petrochenkov

Prefer to_string() to format!()

Simple benchmarks suggest in some cases it can be faster by even 37%:
```
test converting_f64_long  ... bench:         339 ns/iter (+/- 199)
test converting_f64_short ... bench:         136 ns/iter (+/- 34)
test converting_i32_long  ... bench:          87 ns/iter (+/- 16)
test converting_i32_short ... bench:          87 ns/iter (+/- 49)
test converting_str       ... bench:          54 ns/iter (+/- 15)
test formatting_f64_long  ... bench:         349 ns/iter (+/- 176)
test formatting_f64_short ... bench:         145 ns/iter (+/- 14)
test formatting_i32_long  ... bench:          98 ns/iter (+/- 14)
test formatting_i32_short ... bench:          93 ns/iter (+/- 15)
test formatting_str       ... bench:          86 ns/iter (+/- 23)
```

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libsyntax_ext/concat.rs b/src/libsyntax_ext/concat.rs
index 99dba8af754..dcdd2c590e0 100644
--- a/src/libsyntax_ext/concat.rs
+++ b/src/libsyntax_ext/concat.rs
@@ -42,10 +42,10 @@ pub fn expand_syntax_ext(
                 ast::LitKind::Int(i, ast::LitIntType::Unsigned(_))
                 | ast::LitKind::Int(i, ast::LitIntType::Signed(_))
                 | ast::LitKind::Int(i, ast::LitIntType::Unsuffixed) => {
-                    accumulator.push_str(&format!("{}", i));
+                    accumulator.push_str(&i.to_string());
                 }
                 ast::LitKind::Bool(b) => {
-                    accumulator.push_str(&format!("{}", b));
+                    accumulator.push_str(&b.to_string());
                 }
                 ast::LitKind::Byte(..) | ast::LitKind::ByteStr(..) => {
                     cx.span_err(e.span, "cannot concatenate a byte string literal");