Drop ancient Rust <1.31 support code and drop autocfg dependency

Author: paolobarbolini

Cargo.toml

@@ -22,7 +22,6 @@ categories = ["database"]
 duckdb = { version = "=1.3.0", path = "crates/duckdb" }
 libduckdb-sys = { version = "=1.3.0", path = "crates/libduckdb-sys" }
 duckdb-loadable-macros = { version = "=0.1.7", path = "crates/duckdb-loadable-macros" }
-autocfg = "1.0"
 bindgen = { version = "0.71.1", default-features = false }
 calamine = "0.22.0"
 cast = "0.3"

crates/libduckdb-sys/Cargo.toml

@@ -29,7 +29,6 @@ loadable-extension = ["prettyplease", "quote", "syn"]
 [dependencies]
 
 [build-dependencies]
-autocfg = { workspace = true }
 bindgen = { workspace = true, features = ["runtime"], optional = true }
 flate2 = { workspace = true }
 pkg-config = { workspace = true, optional = true }

crates/libduckdb-sys/openssl/mod.rs

@@ -18,7 +18,6 @@
     clippy::unusual_byte_groupings
 )]
 
-extern crate autocfg;
 #[cfg(feature = "openssl_bindgen")]
 extern crate bindgen;
 extern crate cc;
@@ -107,8 +106,6 @@ pub fn get_openssl_v2() -> Result<(Vec<PathBuf>, PathBuf), ()> {
 }
 
 fn get_openssl() -> Result<(Vec<PathBuf>, PathBuf), ()> {
-    check_rustc_versions();
-
     check_ssl_kind()?;
 
     let target = env::var("TARGET").unwrap();
@@ -166,14 +163,6 @@ fn get_openssl() -> Result<(Vec<PathBuf>, PathBuf), ()> {
     Ok((lib_dirs, include_dir))
 }
 
-fn check_rustc_versions() {
-    let cfg = autocfg::new();
-
-    if cfg.probe_rustc_version(1, 31) {
-        println!("cargo:rustc-cfg=const_fn");
-    }
-}
-
 #[allow(clippy::let_and_return)]
 fn postprocess(include_dirs: &[PathBuf]) -> Version {
     let version = validate_headers(include_dirs);