Fix new function_casts_as_integer lint errors in std and compiler crates

Author: GuillaumeGomez

compiler/rustc_driver_impl/src/signal_handler.rs

@@ -152,7 +152,8 @@ pub(super) fn install() {
         libc::sigaltstack(&alt_stack, ptr::null_mut());
 
         let mut sa: libc::sigaction = mem::zeroed();
-        sa.sa_sigaction = print_stack_trace as libc::sighandler_t;
+        sa.sa_sigaction =
+            print_stack_trace as unsafe extern "C" fn(libc::c_int) as libc::sighandler_t;
         sa.sa_flags = libc::SA_NODEFER | libc::SA_RESETHAND | libc::SA_ONSTACK;
         libc::sigemptyset(&mut sa.sa_mask);
         for (signum, _signame) in KILL_SIGNALS {

library/std/src/backtrace.rs

@@ -293,7 +293,7 @@ impl Backtrace {
         if !Backtrace::enabled() {
             return Backtrace { inner: Inner::Disabled };
         }
-        Backtrace::create(Backtrace::capture as usize)
+        Backtrace::create(Backtrace::capture as fn() -> Backtrace as usize)
     }
 
     /// Forcibly captures a full backtrace, regardless of environment variable
@@ -309,7 +309,7 @@ impl Backtrace {
     #[stable(feature = "backtrace", since = "1.65.0")]
     #[inline(never)] // want to make sure there's a frame here to remove
     pub fn force_capture() -> Backtrace {
-        Backtrace::create(Backtrace::force_capture as usize)
+        Backtrace::create(Backtrace::force_capture as fn() -> Backtrace as usize)
     }
 
     /// Forcibly captures a disabled backtrace, regardless of environment

library/std/src/sys/pal/unix/stack_overflow.rs

@@ -169,7 +169,9 @@ mod imp {
                 }
 
                 action.sa_flags = SA_SIGINFO | SA_ONSTACK;
-                action.sa_sigaction = signal_handler as sighandler_t;
+                action.sa_sigaction = signal_handler
+                    as unsafe extern "C" fn(i32, *mut libc::siginfo_t, *mut libc::c_void)
+                    as sighandler_t;
                 // SAFETY: only overriding signals if the default is set
                 unsafe { sigaction(signal, &action, ptr::null_mut()) };
             }