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/testlib/showerror.c

@@ -46,7 +46,7 @@ testonly void testlib_showerror(const char *file, int line, const char *func,
           "\t%s%s\n",
           RED2, UNBOLD, BLUE1, file, (long)line, RESET, method, func,
           g_fixturename, code, v1, symbol, v2, SUBTLE, strerror(errno),
-          program_executable_name, RESET);
+          GetProgramExecutableName(), RESET);
   free_s(&v1);
   free_s(&v2);
 }