LibC: Mark a bunch of functions as cancellation points

Author: https://github.com/timschumi
Commit: c85f307e62
Pull-request: https://github.com/SerenityOS/serenity/pull/14629
Reviewed-by: https://github.com/bgianfo

Userland/Libraries/LibC/stdlib.cpp

@@ -14,6 +14,7 @@
 #include <LibELF/AuxiliaryVector.h>
 #include <alloca.h>
 #include <assert.h>
+#include <bits/pthread_cancel.h>
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -810,6 +811,8 @@ void srandom(unsigned seed)
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/system.html
 int system(char const* command)
 {
+    __pthread_maybe_cancel();
+
     if (!command)
         return 1;