Improve signal handling and math

- Polyfill ucontext_t on FreeBSD/OpenBSD/NetBSD
- Add tests confirming signals can edit CPU state
- Work towards supporting ZIP filesystem on bare metal
- Add more tinymath unit tests for POSIX conformance
- Add X87 and SSE status flags to crash report
- Fix some bugs in blinkenlights
- Fix llvm build breakage

examples/ucontext-sigfpe-recovery.c

@@ -0,0 +1,34 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/calls/calls.h"
+#include "libc/calls/struct/sigaction.h"
+#include "libc/calls/struct/siginfo.h"
+#include "libc/calls/ucontext.h"
+#include "libc/stdio/stdio.h"
+#include "libc/sysv/consts/sa.h"
+#include "libc/sysv/consts/sig.h"
+#include "third_party/xed/x86.h"
+
+void handler(int sig, siginfo_t *si, ucontext_t *ctx) {
+  struct XedDecodedInst xedd;
+  xed_decoded_inst_zero_set_mode(&xedd, XED_MACHINE_MODE_LONG_64);
+  xed_instruction_length_decode(&xedd, (void *)ctx->uc_mcontext.rip, 15);
+  ctx->uc_mcontext.rip += xedd.length;
+  ctx->uc_mcontext.rax = 42;
+  ctx->uc_mcontext.rdx = 0;
+}
+
+int main(int argc, char *argv[]) {
+  struct sigaction saint = {.sa_sigaction = handler, .sa_flags = SA_SIGINFO};
+  sigaction(SIGFPE, &saint, NULL);
+  volatile long x = 0;
+  printf("123/0 = %ld\n", 123 / x);
+  return 0;
+}