feat: add process termination codes and SYS_ABORT; whole-process abort() from any thread in libc and montauk-rt

programs/include/Api/Syscall.hpp

@@ -288,6 +288,11 @@ namespace montauk::abi {
     static constexpr uint64_t FUTEX_WAIT_FOREVER       = ~0ULL;
     static constexpr uint32_t FUTEX_WAKE_ALL           = 0xFFFFFFFFu;
 
+    /* Abnormal termination from any thread: ends the whole process (every
+       thread) with exit code TerminatedAborted (256+SIGABRT). SYS_EXIT from a
+       sibling thread ends only that thread, so abort() needs its own call. */
+    static constexpr uint64_t SYS_ABORT                = 198;  // () -> does not return
+
     /* Kernel-owned process capabilities. User identities may namespace
        per-user resources, but never participate in authorization decisions. */
     static constexpr uint64_t CAP_PROCESS_ADMIN = 1ULL << 0;