Introduce new fatcosmocc command

This new script is an alternative to the `cosmocc` command. It's still a
work in progress. It abstracts all the gory details of building separate
copies of your executable and then running the apelink.com program.

tool/scripts/fat-x86_64

@@ -0,0 +1,56 @@
+#!/bin/sh
+# amd64 backend compiler for fatcosmocc
+
+CC="$COSMO/o/third_party/gcc/bin/x86_64-linux-musl-gcc"
+CCFLAGS="-mno-tls-direct-seg-refs -mno-red-zone"
+LDFLAGS="-static -nostdlib -no-pie -Wl,-melf_x86_64"
+APEFLAGS="-L$COSMOS/lib -Wl,--gc-sections -Wl,-T,$COSMO/o/$MODE/ape/public/ape.lds $COSMO/o/$MODE/ape/ape.o $COSMO/o/$MODE/libc/crt/crt.o"
+LDLIBS="$COSMO/o/$MODE/cosmopolitan.a"
+
+if [ x"$PROG" != x"${PROG%++}" ]; then
+  CC="$COSMO/o/third_party/gcc/bin/x86_64-linux-musl-g++"
+  CCFLAGS="$CCFLAGS -fno-rtti -fno-exceptions -fuse-cxa-atexit -fno-threadsafe-statics"
+  LDLIBS="$COSMO/o/$MODE/third_party/libcxx/libcxx.a $LDLIBS"
+fi
+
+OPT=
+FIRST=1
+OUTPUT=
+INTENT=ld
+for x; do
+  if [ $FIRST -eq 1 ]; then
+    set --
+    FIRST=0
+  fi
+  if [ x"$x" != x"${x#-O}" ]; then
+    OPT=$x
+  elif [ x"$x" = x"-c" ]; then
+    INTENT=cc
+  elif [ x"$x" != x"${x#-o}" ]; then
+    OUTPUT=${x#-o}
+  elif [ x"$x" = x"-march=native" ]; then
+    continue  # doesn't make sense for a cross compiler
+  fi
+  set -- "$@" "$x"
+done
+
+if [ x"$MODE" = x"nox87" ]; then
+  CCFLAGS="$CCFLAGS -mlong-double-64"
+fi
+
+if [ x"$OPT" != x"-Os" ] && [ x"${MODE#tiny}" != x"${MODE}" ]; then
+  # support --ftrace unless optimizing for size
+  CCFLAGS="$CCFLAGS -fpatchable-function-entry=18,16"
+fi
+
+if [ $INTENT = cc ]; then
+  set -- "$CC" $CCFLAGS "$@"
+else
+  set -- "$CC" $CCFLAGS $LDFLAGS $APEFLAGS $CPPFLAGS "$@" \
+         $LDLIBS -Wl,-z,common-page-size=4096 -Wl,-z,max-page-size=4096 \
+         -fuse-ld=bfd
+fi
+
+printf '# %s\n(cd %s; %s)\n' "$ORIGINAL" "$PWD" "$*" >>"${TMPDIR:-/tmp}/build.log"
+"$@" || exit
+"$FIXUPOBJ" "$OUTPUT" || exit