std: expand dlsym! tests

Author: joboet

library/std/src/sys/pal/unix/weak/tests.rs

@@ -2,15 +2,26 @@ use super::*;
 use crate::ffi::c_int;
 
 #[test]
-fn dlsym() {
+fn dlsym_existing() {
     // Try to find a symbol that definitely exists.
     dlsym! {
         fn abs(i: c_int) -> c_int;
     }
 
+    dlsym! {
+        #[link_name = "abs"]
+        fn custom_name(i: c_int) -> c_int;
+    }
+
     let abs = abs.get().unwrap();
     assert_eq!(unsafe { abs(-1) }, 1);
 
+    let custom_name = custom_name.get().unwrap();
+    assert_eq!(unsafe { custom_name(-1) }, 1);
+}
+
+#[test]
+fn dlsym_missing() {
     // Try to find a symbol that definitely does not exist.
     dlsym! {
         fn test_symbol_that_does_not_exist() -> c_int;