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

bin/apecopy

@@ -1,5 +1,4 @@
 #!/bin/sh
-
 PROG=${0##*/}
 COSMO=${COSMO:-/opt/cosmo}
 
@@ -67,8 +66,14 @@ if [ ! -d "$COSMO" ]; then
   fatal_error "you need to clone cosmopolitan to your $COSMO directory"
 fi
 
+if [ -x "$COSMO/o/third_party/gcc/bin/x86_64-linux-musl-gcc" ]; then
+  BRAND=musl
+else
+  BRAND=cosmo
+fi
+
 if [ ! -f "$COSMO/o//tool/build/zipcopy.com" ] ||
-   [ ! -f "$COSMO/o/third_party/gcc/bin/$ARCH-linux-musl-objcopy" ]; then
+   [ ! -f "$COSMO/o/third_party/gcc/bin/$ARCH-linux-$BRAND-objcopy" ]; then
   if [ $CROSS -eq 0 ]; then
     fatal_error "you need to run: cosmocc --update"
   else
@@ -88,7 +93,7 @@ elif [ x"$INPUT" = x"$OUTPUT" ]; then
   fatal_error "$INPUT: input and output file can't be the same"
 fi
 
-"$COSMO/o/third_party/gcc/bin/$ARCH-linux-musl-objcopy" \
+"$COSMO/o/third_party/gcc/bin/$ARCH-linux-$BRAND-objcopy" \
   $OBJCOPYFLAGS \
   "$INPUT" \
   "$OUTPUT" || exit