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/definitions.lua

@@ -1196,6 +1196,10 @@ function GetHost() end
 ---@nodiscard
 function GetHostOs() end
 
+---@return "X86_64"|"AARCH64"|"POWERPC64"|"S390X" isaname string that describes the host instruction set architecture
+---@nodiscard
+function GetHostIsa() end
+
 ---@param str string|integer monospace display width of string.
 --- This is useful for fixed-width formatting. For example, CJK characters
 --- typically take up two cells. This function takes into consideration combining