Add postgres19 compatibility

```
src/hll.c: In function 'InitializeHllAggregateOids':src/hll.c:237:1: error: old-style function definition [-Werror=old-style-definition] 237 | InitializeHllAggregateOids() | ^~~~~~~~~~~~~~~~~~~~~~~~~~src/hll.c: In function

'FunctionOid':src/hll.c:342:24: error: too few arguments to function 'FuncnameGetCandidates' 342 | functionList = FuncnameGetCandidates(qualifiedFunctionNameList, argumentCount, | ^~~~~~~~~~~~~~~~~~~~~In file included from src/hll.c:56:/postgres/include/server/catalog/namespace.h:119:26: note: declared here 119 | extern FuncCandidateList FuncnameGetCandidates(List *names, | ^~~~~~~~~~~~~~~~~~~~~In file included from /usr/include/features.h:423, from /usr/include/assert.h:35,

from error: expected specifier-qualifier-list before 'extern'1034 | ((void) sizeof(struct {static_assert(condition, errmessage); char a;})) | ^~~~~~~~~~~~~//

/postgres/include/server/utils/memutils.h:125:10: note: in expansion of macro 'StaticAssertExpr' 125 | (StaticAssertExpr(__builtin_constant_p(name), \ | ^~~~~~~~~~~~~~~~src/hll.c:3159:18: note: in expansion of macro 'AllocSetContextCreate'3159 | tmpcontext = AllocSetContextCreate(rcontext, | ^~~~~~~~~~~~~~~~~~~~~cc1: all warnings being treated as errorsmake: *** [: src/hll.o] Error
```

postgresql-hll fails to compile with pg19 with 3 errors:

1.old-style function definition (-Werror=old-style-definition),
2. FuncnameGetCandidates() gained a new int *fgc_flags parameter
3. AllocSetContextCreate macro uses C23 static_assert incompatible with GCC 12. Even after fixing compilation, passing NULL for fgc_flags causes a server crash (segfault) since PG19 unconditionally dereferences it.