Make improvements

- You can now run `make -j8 toolchain` on Windows
- You can now run `make -j` on MacOS ARM64 and BSD OSes
- You can now use our Emacs dev environment on MacOS/Windows
- Fix bug where the x16 register was being corrupted by --ftrace
- The programs under build/bootstrap/ are updated as fat binaries
- The Makefile now explains how to download cosmocc-0.0.12 toolchain
- The build scripts under bin/ now support "cosmo" branded toolchains
- stat() now goes faster on Windows (shaves 100ms off `make` latency)
- Code cleanup and added review on the Windows signal checking code
- posix_spawnattr_setrlimit() now works around MacOS ARM64 bugs
- Landlock Make now favors posix_spawn() on non-Linux/OpenBSD
- posix_spawn() now has better --strace logging on Windows
- fstatat() can now avoid EACCES in more cases on Windows
- fchmod() can now change the readonly bit on Windows

libc/integral/c.inc

@@ -146,7 +146,6 @@ typedef struct {
 } axdx_t;
 #endif
 
-
 #ifndef __chibicc__
 #define va_list            __builtin_va_list
 #define va_arg(ap, type)   __builtin_va_arg(ap, type)
@@ -620,12 +619,6 @@ void abort(void) wontreturn;
   do {            \
   } while (0)
 
-#if defined(__GNUC__) && !defined(__STRICT_ANSI__)
-#define _Vector_size(k) __attribute__((__vector_size__(k)))
-#else
-#define _Vector_size(k) [k]
-#endif
-
 #ifndef __STRICT_ANSI__
 #define textstartup _Section(".text.startup")
 #define textexit    _Section(".text.exit")