Make improvements

This change progresses our AARCH64 support:

- The AARCH64 build and tests are now passing
- Add 128-bit floating-point support to printf()
- Fix clone() so it initializes cosmo's x28 TLS register
- Fix TLS memory layout issue with aarch64 _Alignas vars
- Revamp microbenchmarking tools so they work on aarch64
- Make some subtle improvements to aarch64 crash reporting
- Make kisdangerous() memory checks more accurate on aarch64
- Remove sys_open() since it's not available on Linux AARCH64

This change makes general improvements to Cosmo and Redbean:

- Introduce GetHostIsa() function in Redbean
- You can now feature check using pledge(0, 0)
- You can now feature check using unveil("",0)
- Refactor some more x86-specific asm comments
- Refactor and write docs for some libm functions
- Make the mmap() API behave more similar to Linux
- Fix WIFSIGNALED() which wrongly returned true for zero
- Rename some obscure cosmo keywords from noFOO to dontFOO

libc/calls/openpty.c

@@ -32,6 +32,7 @@
 #include "libc/intrin/kprintf.h"
 #include "libc/log/rop.h"
 #include "libc/str/str.h"
+#include "libc/sysv/consts/at.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/pty.h"
 #include "libc/sysv/consts/termios.h"
@@ -55,7 +56,7 @@ static int openpty_impl(int *mfd, int *sfd, char *name,
     RETURN_ON_ERROR(grantpt(m));
     RETURN_ON_ERROR(unlockpt(m));
     RETURN_ON_ERROR(_ptsname(m, t.sname, sizeof(t.sname)));
-    RETURN_ON_ERROR((s = sys_open(t.sname, O_RDWR, 0)));
+    RETURN_ON_ERROR((s = sys_openat(AT_FDCWD, t.sname, O_RDWR, 0)));
   } else {
     RETURN_ON_ERROR(sys_ioctl(m, PTMGET, &t));
     close(m);