Fix memory leak of gsymbol

We did not free global symbols. For a simplified abstract_type_3.f90
valgrind reports:

96 bytes in 1 blocks are still reachable in loss record 461 of 602
   at 0x48377D5: calloc (vg_replace_malloc.c:711)
   by 0x21257C3: xcalloc (xmalloc.c:162)
   by 0x98611B: gfc_get_gsymbol(char const*) (symbol.c:4341)
   by 0x932C58: parse_module() (parse.c:5912)
   by 0x9336F8: gfc_parse_file() (parse.c:6236)
   by 0x991449: gfc_be_parse_file() (f95-lang.c:204)
   by 0x11D8EDE: compile_file() (toplev.c:455)
   by 0x11DB9C3: do_compile() (toplev.c:2170)
   by 0x11DBCAF: toplev::main(int, char**) (toplev.c:2305)
   by 0x2045D37: main (main.c:39)

This patch reduces this to

 LEAK SUMMARY:
    definitely lost: 344 bytes in 1 blocks
    indirectly lost: 3,024 bytes in 4 blocks
      possibly lost: 0 bytes in 0 blocks
-   still reachable: 1,576,174 bytes in 2,277 blocks
+   still reachable: 1,576,078 bytes in 2,276 blocks
         suppressed: 0 bytes in 0 blocks

gcc/fortran/ChangeLog:

2018-10-21  Bernhard Reutner-Fischer  <aldot@gcc.gnu.org>

	* parse.c (clean_up_modules): Free gsym.
1 file changed