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/intrin/asan.c

@@ -1400,7 +1400,7 @@ void __asan_map_shadow(uintptr_t p, size_t n) {
       }
     }
     size = (size_t)i << 16;
-    addr = (void *)(intptr_t)((int64_t)((uint64_t)a << 32) >> 16);
+    addr = (void *)ADDR_32_TO_48(a);
     prot = PROT_READ | PROT_WRITE;
     flag = MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS;
     sm = _weaken(sys_mmap)(addr, size, prot, flag, -1, 0);
@@ -1413,8 +1413,7 @@ void __asan_map_shadow(uintptr_t p, size_t n) {
       __asan_die()();
       __asan_unreachable();
     }
-    __repstosb((void *)(intptr_t)((int64_t)((uint64_t)a << 32) >> 16),
-               kAsanUnmapped, size);
+    __repstosb(addr, kAsanUnmapped, size);
   }
   __asan_unpoison((char *)p, n);
 }