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/dtime.c

@@ -18,6 +18,8 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/struct/timespec.h"
 
+// TODO(jart): DELETE
+
 /**
  * Returns seconds since epoch w/ high-precision.
  * @param clockid can be CLOCK_{REALTIME,MONOTONIC}, etc.
@@ -27,7 +29,7 @@ long double dtime(int clockid) {
   struct timespec tv;
   clock_gettime(clockid, &tv);
   secs = tv.tv_nsec;
-  secs *= 1 / 1e9;
+  secs *= 1e-9;
   secs += tv.tv_sec;
   return secs;
 }