Fix this by allowing these module functions and variables to be missing.
Tested on x86_64-linux with gcc 4.8.5 and gcc 7.5.0.
gdb/testsuite/ChangeLog:
2020-07-30 Tom de Vries <tdevries@suse.de>
* lib/sym-info-cmds.exp (GDBInfoModuleSymbols::check_entry_1): Factor
out of ...
(GDBInfoModuleSymbols::check_entry): ... here.
(GDBInfoModuleSymbols::check_optional_entry): New proc.
* gdb.fortran/info-modules.exp: Use check_optional_entry for entries
related to __def_init_mod1_M1t1 / __vtype_mod1_M1t1 / __copy_mod1_M1t1.