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/intrin/macros.h

@@ -9,7 +9,8 @@
 
 #if defined(__x86_64__) && !defined(__STRICT_ANSI__)
 
-typedef char __intrin_xmm_t _Vector_size(16) forcealign(16) mayalias;
+typedef char __intrin_xmm_t
+    __attribute__((__vector_size__(16), __aligned__(16), __may_alias__));
 
 #define INTRIN_SSEVEX_X_X_X_(PURE, ISA, OP, FLAGS, A, B, C)                    \
   do {                                                                         \