Fix link failure when building on Fedora 64bit

Fedora and other Linux distributions tend to use `lib64` as the library
directory and when building and installing the native library with CMake
the directory structure in the prefix conforms to this standard.

This makes the linking fail since the search directory for `libnng` is
set to `lib`.

This patch renames `lib64` to `lib` in the install directory. There are
no checks performed beforehand since the Rust API already checks that
the operation can be performed, and if the rename fails then the
directory name is already correct.

The same issue is also present for `mbedtls` and was fixed there as
well.

Author: kicsyromy

build.rs

@@ -194,6 +194,11 @@ fn build_mbedtls(nng: &mut cmake::Config, is_ninja: bool) {
 
     let mut dest = config.build();
 
+    // On some 64bit Linux distributions the library directory is `lib64`
+    // instead of `lib`. Rename it in the name of consistency.
+    #[cfg(target_os = "linux")]
+    let _ = std::fs::rename(dest.as_path().join("lib64"), dest.as_path().join("lib"));
+
     nng.define("MBEDTLS_ROOT_DIR", &dest);
 
     dest.push("lib");
@@ -274,6 +279,12 @@ fn build() {
 
     println!("cargo:rustc-link-lib=static=nng");
     let mut dest = config.build();
+
+    // On some 64bit Linux distributions the library directory is `lib64`
+    // instead of `lib`. Rename it in the name of consistency.
+    #[cfg(target_os = "linux")]
+    let _ = std::fs::rename(dest.as_path().join("lib64"), dest.as_path().join("lib"));
+
     dest.push("lib");
     println!("cargo:rustc-link-search=native={}", dest.display());
 }