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

libc/calls/fstat-metal.c

@@ -22,7 +22,7 @@
 #include "libc/sysv/consts/s.h"
 #include "libc/sysv/errfuns.h"
 
-int fstat_metal(int fd, struct stat *st) {
+int sys_fstat_metal(int fd, struct stat *st) {
   if (fd < 0) return einval();
   if (fd < g_fds.n && g_fds.p[fd].kind == kFdSerial) {
     memset(st, 0, sizeof(*st));