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!

libc/runtime/fork-nt.c

@@ -291,7 +291,7 @@ textwindows int sys_fork_nt(void) {
         args = args2;
       }
 #endif
-      if (ntspawn(program_executable_name, args, environ, forkvar,
+      if (ntspawn(GetProgramExecutableName(), args, environ, forkvar,
                   &kNtIsInheritable, NULL, true, 0, NULL, &startinfo,
                   &procinfo) != -1) {
         CloseHandle(reader);