Prove that Makefile is fully defined

The whole repository is now buildable with GNU Make Landlock sandboxing.
This proves that no Makefile targets exist which touch files other than
their declared prerequisites. In order to do this, we had to:

  1. Stop code morphing GCC output in package.com and instead run a
     newly introduced FIXUPOBJ.COM command after GCC invocations.

  2. Disable all the crumby Python unit tests that do things like create
     files in the current directory, or rename() files between folders.
     This ended up being a lot of tests, but most of them are still ok.

  3. Introduce an .UNSANDBOXED variable to GNU Make to disable Landlock.
     We currently only do this for things like `make tags`.

  4. This change deletes some GNU Make code that was preventing the
     execve() optimization from working. This means it should no longer
     be necessary in most cases for command invocations to be indirected
     through the cocmd interpreter.

  5. Missing dependencies had to be declared in certain places, in cases
     where they couldn't be automatically determined by MKDEPS.COM

  6. The libcxx header situation has finally been tamed. One of the
     things that makes this difficult is MKDEPS.COM only wants to
     consider the first 64kb of a file, in order to go fast. But libcxx
     likes to have #include lines buried after huge documentation.

  7. An .UNVEIL variable has been introduced to GNU Make just in case
     we ever wish to explicitly specify additional things that need to
     be whitelisted which aren't strictly prerequisites. This works in
     a manner similar to the recently introduced .EXTRA_PREREQS feature.

There's now a new build/bootstrap/make.com prebuilt binary available. It
should no longer be possible to write invalid Makefile code.

libc/sock/struct/ifconf.h

@@ -0,0 +1,27 @@
+#ifndef COSMOPOLITAN_LIBC_SOCK_STRUCT_IFCONF_H_
+#define COSMOPOLITAN_LIBC_SOCK_STRUCT_IFCONF_H_
+#include "libc/sock/struct/ifreq.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+/*
+ * Structure used in SIOCGIFCONF request.
+ * Used to retrieve interface configuration
+ * for machine (useful for programs which
+ * must know all networks accessible).
+ */
+struct ifconf {
+  uint64_t ifc_len; /* size of buffer   */
+  union {
+    char *ifcu_buf;
+    struct ifreq *ifcu_req;
+  } ifc_ifcu;
+};
+
+/* Shortcuts to the ifconf buffer or ifreq array */
+#define ifc_buf ifc_ifcu.ifcu_buf /* buffer address   */
+#define ifc_req ifc_ifcu.ifcu_req /* array of structures  */
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_IFCONF_H_ */

libc/sock/struct/ifreq.h

@@ -0,0 +1,30 @@
+#ifndef COSMOPOLITAN_LIBC_SOCK_STRUCT_IFREQ_H_
+#define COSMOPOLITAN_LIBC_SOCK_STRUCT_IFREQ_H_
+#include "libc/sock/struct/sockaddr.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+struct ifreq {
+  union {
+    char ifrn_name[IFNAMSIZ]; /* Interface name, e.g. "en0".  */
+  } ifr_ifrn;
+  union {
+    struct sockaddr ifru_addr;      /* SIOCGIFADDR */
+    struct sockaddr ifru_dstaddr;   /* SIOCGIFDSTADDR */
+    struct sockaddr ifru_netmask;   /* SIOCGIFNETMASK */
+    struct sockaddr ifru_broadaddr; /* SIOCGIFBRDADDR */
+    short ifru_flags;               /* SIOCGIFFLAGS */
+    char ifru_pad[24];              /* ifru_map is the largest, just pad */
+  } ifr_ifru;
+};
+
+#define ifr_name      ifr_ifrn.ifrn_name /* interface name */
+#define ifr_addr      ifr_ifru.ifru_addr /* address */
+#define ifr_netmask   ifr_ifru.ifru_netmask /* netmask */
+#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
+#define ifr_dstaddr   ifr_ifru.ifru_dstaddr /* destination address */
+#define ifr_flags     ifr_ifru.ifru_flags /* flags */
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_IFREQ_H_ */

libc/sock/struct/ip_mreq.h

@@ -0,0 +1,13 @@
+#ifndef COSMOPOLITAN_LIBC_SOCK_STRUCT_IP_MREQ_H_
+#define COSMOPOLITAN_LIBC_SOCK_STRUCT_IP_MREQ_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+struct ip_mreq {
+  struct in_addr imr_multiaddr; /* IP multicast address of group */
+  struct in_addr imr_interface; /* local IP address of interface */
+};
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_IP_MREQ_H_ */

libc/sock/struct/msghdr.h

@@ -14,6 +14,9 @@ struct msghdr {            /* Linux+NT ABI */
   uint32_t msg_flags;      /* MSG_XXX */
 };
 
+ssize_t recvmsg(int, struct msghdr *, int);
+ssize_t sendmsg(int, const struct msghdr *, int);
+
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_MSGHDR_H_ */

libc/sock/struct/pollfd.h

@@ -9,6 +9,8 @@ struct pollfd {
   int16_t revents;
 };
 
+int poll(struct pollfd *, uint64_t, int32_t);
+
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_POLLFD_H_ */

libc/sock/struct/sockaddr.h

@@ -33,6 +33,9 @@ struct sockaddr_storage {
   };
 };
 
+int inet_aton(const char *, struct in_addr *);
+char *inet_ntoa(struct in_addr);
+
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_SOCK_STRUCT_SOCKADDR_H_ */