Fix type_stack leaks in c expression parsing.

Fix type_stack leaks in c expression parsing.

Valgrind detects a bunch of leaks in several tests, such as:

==22905== 40 (24 direct, 16 indirect) bytes in 1 blocks are definitely lost in loss record 531 of 3,268
==22905==    at 0x4C2C4CC: operator new(unsigned long) (vg_replace_malloc.c:344)
==22905==    by 0x5893AD: get_type_stack() (parse.c:1509)
==22905==    by 0x3F4EAD: c_yyparse() (c-exp.y:1223)
==22905==    by 0x3F71BC: c_parse(parser_state*) (c-exp.y:3308)
==22905==    by 0x588CEA: parse_exp_in_context_1(char const**, unsigned long, block const*, int, int, int*) [clone .constprop.89] (parse.c:1205)
==22905==    by 0x588FA1: parse_exp_in_context (parse.c:1108)
==22905==    by 0x588FA1: parse_exp_1 (parse.c:1099)
==22905==    by 0x588FA1: parse_expression(char const*) (parse.c:1247)
...

==22395== 456 (168 direct, 288 indirect) bytes in 7 blocks are definitely lost in loss record 2,658 of 2,978
==22395==    at 0x4C2C4CC: operator new(unsigned long) (vg_replace_malloc.c:344)
==22395==    by 0x5893AD: get_type_stack() (parse.c:1509)
==22395==    by 0x3F4ECF: c_yyparse() (c-exp.y:1230)
==22395==    by 0x3F71BC: c_parse(parser_state*) (c-exp.y:3308)
==22395==    by 0x588CEA: parse_exp_in_context_1(char const**, unsigned long, block const*, int, int, int*) [clone .constprop.89] (parse.c:1205)
==22395==    by 0x588FA1: parse_exp_in_context (parse.c:1108)
==22395==    by 0x588FA1: parse_exp_1 (parse.c:1099)
==22395==    by 0x588FA1: parse_expression(char const*) (parse.c:1247)
==22395==    by 0x67BB9D: whatis_exp(char const*, int) (typeprint.c:515)
...

==22395== VALGRIND_GDB_ERROR_BEGIN
==22395== 144 (24 direct, 120 indirect) bytes in 1 blocks are definitely lost in loss record 1,016 of 2,978
==22395==    at 0x4C2C4CC: operator new(unsigned long) (vg_replace_malloc.c:344)
==22395==    by 0x5893AD: get_type_stack() (parse.c:1509)
==22395==    by 0x3F4E8A: c_yyparse() (c-exp.y:1217)
==22395==    by 0x3F71BC: c_parse(parser_state*) (c-exp.y:3308)
==22395==    by 0x588CEA: parse_exp_in_context_1(char const**, unsigned long, block const*, int, int, int*) [clone .constprop.89] (parse.c:1205)
==22395==    by 0x588FA1: parse_exp_in_context (parse.c:1108)
==22395==    by 0x588FA1: parse_exp_1 (parse.c:1099)
==22395==    by 0x588FA1: parse_expression(char const*) (parse.c:1247)
==22395==    by 0x67BB9D: whatis_exp(char const*, int) (typeprint.c:515)
...

Fix these by storing the allocated type_stack in the cpstate->type_stacks
vector.

Tested on debian/amd64, natively and under valgrind.

gdb/ChangeLog
2019-02-10  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* c-exp.y (direct_abs_decl): Use emplace_back to record the
	type_stack.