Auto merge of rust-lang#138775 - oli-obk:perf-check, r=<try>

Avoid sending a non-null pointer for empty strings

Another try at fixing the perf regression from rust-lang#138674

r? `@ghost`

Author: bors

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -643,10 +643,10 @@ fn create_file<'ll>(
             builder,
             file_name.as_c_char_ptr(),
             file_name.len(),
-            directory.as_c_char_ptr(),
+            if directory.is_empty() { ptr::null() } else { directory.as_c_char_ptr() },
             directory.len(),
             hash_kind,
-            hash_value.as_c_char_ptr(),
+            if hash_value.is_empty() { ptr::null() } else { hash_value.as_c_char_ptr() },
             hash_value.len(),
             source.map_or(ptr::null(), |x| x.as_c_char_ptr()),
             source.map_or(0, |x| x.len()),