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/calls/assertfail.c

@@ -18,6 +18,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
 #include "libc/calls/calls.h"
+#include "libc/calls/struct/sigset.internal.h"
 #include "libc/errno.h"
 #include "libc/fmt/itoa.h"
 #include "libc/intrin/describebacktrace.internal.h"
@@ -28,9 +29,11 @@
  */
 void __assert_fail(const char *expr, const char *file, int line) {
   char ibuf[12];
+  sigset_t m = __sig_block();
   FormatInt32(ibuf, line);
   tinyprint(2, file, ":", ibuf, ": assert(", expr, ") failed (",
             program_invocation_short_name, " ",
             DescribeBacktrace(__builtin_frame_address(0)), ")\n", NULL);
+  __sig_unblock(m);
   abort();
 }