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/tls.h

@@ -66,7 +66,11 @@ void __set_tls(struct CosmoTib *);
   })
 #define __adj_tls(tib) (tib)
 #elif defined(__aarch64__)
-#define __get_tls()    ((struct CosmoTib *)__builtin_thread_pointer() - 1)
+#define __get_tls()                          \
+  ({                                         \
+    register struct CosmoTib *_t asm("x28"); \
+    _t - 1;                                  \
+  })
 #define __adj_tls(tib) ((struct CosmoTib *)(tib) + 1)
 #endif