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/calls/calls.h

@@ -50,11 +50,11 @@
 #define MAP_HUGE_2MB (21 << MAP_HUGE_SHIFT)
 #define MAP_HUGE_1GB (30 << MAP_HUGE_SHIFT)
 
-#define WCOREDUMP(s)    (0x80 & (s))
+#define WCOREDUMP(s)    (128 & (s))
 #define WEXITSTATUS(s)  ((0xff00 & (s)) >> 8)
 #define WIFCONTINUED(s) ((s) == 0xffff)
 #define WIFEXITED(s)    (!WTERMSIG(s))
-#define WIFSIGNALED(s)  ((0xffff & (s)) - 1u < 0xffu)
+#define WIFSIGNALED(s)  (((signed char)((127 & (s)) + 1) >> 1) > 0)
 #define WIFSTOPPED(s)   ((255 & (s)) == 127)
 #define WSTOPSIG(s)     WEXITSTATUS(s)
 #define WTERMSIG(s)     (127 & (s))