Fix invalid cfg flags

Author: b-NC

tests/pass/libc.rs

@@ -252,7 +252,6 @@ fn test_clocks() {
     assert_eq!(is_error, 0);
 }
 
-#[cfg(target_os = "linux, macos")]
 fn test_getpid() {
     unsafe {
         assert_eq!(libc::getpid(), std::process::id());
@@ -282,6 +281,5 @@ fn main() {
     #[cfg(target_os = "linux")]
     test_clocks();
 
-    #[cfg(target_os = "linux, macos")]
     test_getpid();
 }