Add support for symbol table in .com files

This change fixes minor bugs and adds a feature, which lets us store the
ELF symbol table, inside the ZIP directory. We use the path /zip/.symtab
which can be safely removed using a zip editing tool, to make the binary
smaller after compilation. This supplements the existing method of using
a separate .com.dbg file, which is still supported. The intent is people
don't always know that it's a good idea to download the debug file. It's
not great having someone's first experience be a crash report, that only
has numbers rather than symbols. This will help fix that!

tool/build/symtab.c

@@ -0,0 +1,99 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/errno.h"
+#include "libc/intrin/kprintf.h"
+#include "libc/runtime/runtime.h"
+#include "libc/runtime/symbols.internal.h"
+#include "libc/stdio/stdio.h"
+#include "libc/sysv/consts/ex.h"
+#include "libc/sysv/consts/exit.h"
+#include "libc/sysv/consts/o.h"
+#include "third_party/getopt/getopt.h"
+
+/**
+ * @fileoverview elf to symbol table file dump tool
+ */
+
+void PrintUsage(FILE *f) {
+  fprintf(f, "%s%s%s\n", "usage: ", program_invocation_name,
+          " [-?h] -o PATH COMDBG");
+}
+
+int main(int argc, char *argv[]) {
+  int fd, opt;
+  const char *outpath;
+  struct SymbolTable *tab;
+
+  outpath = 0;
+
+  while ((opt = getopt(argc, argv, "?ho:")) != -1) {
+    switch (opt) {
+      case 'o':
+        outpath = optarg;
+        break;
+      case '?':
+      case 'h':
+        PrintUsage(stdout);
+        return 0;
+      default:
+        PrintUsage(stderr);
+        return EX_USAGE;
+    }
+  }
+
+  if (!outpath) {
+    fprintf(stderr, "error: need output path\n");
+    PrintUsage(stderr);
+    return 1;
+  }
+
+  if (optind + 1 != argc) {
+    fprintf(stderr, "error: need exactly one input path\n");
+    PrintUsage(stderr);
+    return 2;
+  }
+
+  if (!(tab = OpenSymbolTable(argv[optind]))) {
+    fprintf(stderr, "error: %s(%`'s) failed %m\n", "OpenSymbolTable",
+            argv[optind]);
+    return 3;
+  }
+
+  tab->names = 0;
+  tab->name_base = 0;
+
+  if ((fd = open(outpath, O_WRONLY | O_CREAT | O_TRUNC, 0644)) == -1) {
+    fprintf(stderr, "error: %s(%`'s) failed %m\n", "open", outpath);
+    return 4;
+  }
+
+  if (write(fd, (const char *)tab, tab->size) != tab->size) {
+    fprintf(stderr, "error: %s(%`'s) failed %m\n", "write", outpath);
+    return 5;
+  }
+
+  if (close(fd) == -1) {
+    fprintf(stderr, "error: %s(%`'s) failed %m\n", "close", outpath);
+    return 6;
+  }
+
+  CloseSymbolTable(&tab);
+  return 0;
+}