fix/uutils ~ support function/util (aka, applet) symlink aliasing where possible

## [why]

`std::env::current_exe()` has platform dependent behavior and will often
return the target binary, not the symlink name, when the binary is executed
via symlink. So, to support symlinking, the first (0th) arg from `std::env::args()`
is used, when possible, with fallback to `std::env::current_ext()` if args are
missing or empty.

- ref: <https://github.com/rust-lang/rust/issues/43617>

src/bin/uutils.rs

@@ -10,7 +10,7 @@
 // spell-checker:ignore (acronyms/names) Gehring
 // spell-checker:ignore (rustlang) clippy concat rustlang
 // spell-checker:ignore (uutils) coreutils uucore uumain uutils sigpipe
-// spell-checker:ignore (shell) busybox
+// spell-checker:ignore (shell) busybox symlinks
 
 include!(concat!(env!("OUT_DIR"), "/uutils_crates.rs"));
 
@@ -24,7 +24,13 @@ use std::io::Write;
 static VERSION: &str = env!("CARGO_PKG_VERSION");
 
 lazy_static! {
-    static ref BINARY_PATH: std::path::PathBuf = std::env::current_exe().unwrap();
+    static ref BINARY_PATH: std::path::PathBuf = {
+        // support symlinks by using args[0], when possible, with fallback to current_exe()
+        match std::env::args().next() {
+            Some(ref s) if !s.is_empty() => std::path::PathBuf::from(s),
+            _ => std::env::current_exe().unwrap(),
+        }
+    };
     static ref NAME: &'static str = &*BINARY_PATH.file_stem().unwrap().to_str().unwrap();
 }