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/readv-serial.c

@@ -34,7 +34,7 @@ static int GetFirstIov(struct iovec *iov, int iovlen) {
   return -1;
 }
 
-ssize_t readv_serial(struct Fd *fd, const struct iovec *iov, int iovlen) {
+ssize_t sys_readv_serial(struct Fd *fd, const struct iovec *iov, int iovlen) {
   size_t i, j, got = 0;
   if ((i = GetFirstIov(iov, iovlen)) != -1) {
     while (!IsDataAvailable(fd)) asm("pause");