[kernel] Move kassert out of kutil

Continuing moving things out of kutil. The assert as implemented could
only ever work in the kernel, so remaining kutil uses of kassert have
been moved to including standard C assert instead.

Along the way, kassert was broken out into panic::panic and kassert,
and the panic.serial namespace was renamed panicking.

src/kernel/assert.h

@@ -0,0 +1,61 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace panic {
+
+constexpr uint32_t send_nmi_command =
+    (4 << 8) |  // Delivery mode NMI
+    (1 << 14) | // assert level high
+    (1 << 18);  // destination self
+
+extern uint32_t *apic_icr;
+extern uintptr_t symbol_table;
+
+__attribute__ ((always_inline))
+inline void panic(
+        const char *message = nullptr,
+        const char *function = __builtin_FUNCTION(),
+        const char *file = __builtin_FILE(),
+        uint64_t line = __builtin_LINE())
+{
+    register uintptr_t syms asm("rdi");
+    register const char *m asm("rsi");
+    register const char *fn asm("rdx");
+    register const char *fi asm("rcx");
+    register uint64_t l asm("r8");
+
+    asm volatile ("mov %1, %0" : "=r"(syms) : "r"(symbol_table));
+    asm volatile ("mov %1, %0" : "=r"(m) : "r"(message));
+    asm volatile ("mov %1, %0" : "=r"(fn) : "r"(function));
+    asm volatile ("mov %1, %0" : "=r"(fi) : "r"(file));
+    asm volatile ("mov %1, %0" : "=r"(l) : "r"(line));
+
+    *apic_icr = send_nmi_command;
+    while (1) asm ("hlt");
+}
+
+} // namespace panic
+
+#ifndef NDEBUG
+
+__attribute__ ((always_inline))
+inline void kassert(
+        bool check,
+        const char *message = nullptr,
+        const char *function = __builtin_FUNCTION(),
+        const char *file = __builtin_FILE(),
+        uint64_t line = __builtin_LINE())
+{
+    if (!check)
+        panic::panic(message, function, file, line);
+}
+
+#define assert(x) kassert((x))
+
+#else // NDEBUG
+
+#define kassert(...) ((void)0)
+#define assert(x) ((void)0)
+
+#endif // NDEBUG