LibCore: Add syscall wrapper for mkstemp()

Userland/Libraries/LibCore/System.cpp

@@ -488,4 +488,12 @@ ErrorOr<pid_t> fork()
     return pid;
 }
 
+ErrorOr<int> mkstemp(Span<char> pattern)
+{
+    int fd = ::mkstemp(pattern.data());
+    if (fd < 0)
+        return Error::from_syscall("mkstemp"sv, -errno);
+    return fd;
+}
+
 }

Userland/Libraries/LibCore/System.h

@@ -65,5 +65,6 @@ ErrorOr<bool> isatty(int fd);
 ErrorOr<void> symlink(StringView target, StringView link_path);
 ErrorOr<void> mkdir(StringView path, mode_t);
 ErrorOr<pid_t> fork();
+ErrorOr<int> mkstemp(Span<char> pattern);
 
 }