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

tool/net/lfuncs.c

@@ -213,6 +213,23 @@ int LuaGetHostOs(lua_State *L) {
   return 1;
 }
 
+int LuaGetHostIsa(lua_State *L) {
+  const char *s;
+#ifdef __x86_64__
+  s = "X86_64";
+#elif defined(__aarch64__)
+  s = "AARCH64";
+#elif defined(__powerpc64__)
+  s = "POWERPC64";
+#elif defined(__s390x__)
+  s = "S390X";
+#else
+#error "unsupported architecture"
+#endif
+  lua_pushstring(L, s);
+  return 1;
+}
+
 int LuaFormatIp(lua_State *L) {
   char b[16];
   uint32_t ip;