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

tool/build/build.mk

@@ -108,6 +108,7 @@ o/$(MODE)/tool/build/dso/sandbox.so:			\
 		-s					\
 		-shared					\
 		-nostdlib				\
+		-fuse-ld=bfd				\
 		-Wl,--gc-sections			\
 		o/$(MODE)/tool/build/dso/sandbox.o	\
 		o/$(MODE)/libc/calls/pledge-linux.o	\