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/thread/pthread_getname_np.c

@@ -26,6 +26,7 @@
 #include "libc/intrin/atomic.h"
 #include "libc/macros.internal.h"
 #include "libc/str/str.h"
+#include "libc/sysv/consts/at.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/consts/pr.h"
 #include "libc/thread/posixthread.internal.h"
@@ -52,7 +53,7 @@ static errno_t pthread_getname_impl(pthread_t thread, char *name, size_t size) {
       p = stpcpy(p, "/proc/self/task/");
       p = FormatUint32(p, tid);
       p = stpcpy(p, "/comm");
-      if ((fd = sys_open(path, O_RDONLY | O_CLOEXEC, 0)) == -1) {
+      if ((fd = sys_openat(AT_FDCWD, path, O_RDONLY | O_CLOEXEC, 0)) == -1) {
         rc = errno;
         errno = e;
         return rc;