PG19: error: expected identifier or ‘(’ before ‘void’

The PG19/v1.8.0-rc0 doesn't work with PG 19 beta 2:

```
x86_64-linux-gnu-gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wmissing-format-attribute -Wold-style-declaration -Wimplicit-fallthrough=5 -Wcast-function-type -Wshadow=compatible-local -Wformat-security -Wmissing-variable-declarations -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -g -g -O2 -Werror=implicit-function-declaration -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -fno-omit-frame-pointer -Wstrict-prototypes -Wold-style-definition -g -O2 -Werror=implicit-function-declaration -ffile-prefix-map=/home/myon/projects/postgresql/postgresql-age/postgresql-age=. -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -fPIC -fvisibility=hidden -MMD -MP -I.//src/include -I.//src/include/parser -I. -I./ -I/usr/include/postgresql/19/server -I/usr/include/postgresql/internal -Wdate-time -D_FORTIFY_SOURCE=2 -D_GNU_SOURCE -I/usr/include/libxml2 -c -o src/backend/utils/graph_generation.o src/backend/utils/graph_generation.c
src/backend/utils/adt/agtype_parser.c:77:1: warning: ‘noreturn’ attribute ignored [-Wattributes]
77 | static pg_noreturn void report_parse_error(agtype_parse_context ctx,
| ^~~~~~
src/backend/utils/adt/agtype_parser.c:77:20: error: expected identifier or ‘(’ before ‘void’
77 | static pg_noreturn void report_parse_error(agtype_parse_context ctx,
| ^~~~
src/backend/utils/adt/agtype_parser.c:79:1: warning: ‘noreturn’ attribute ignored [-Wattributes]
79 | static pg_noreturn void report_invalid_token(agtype_lex_context *lex);
| ^~~~~~
src/backend/utils/adt/agtype_parser.c:79:20: error: expected identifier or ‘(’ before ‘void’
79 | static pg_noreturn void report_invalid_token(agtype_lex_context *lex);
| ^~~~
src/backend/utils/adt/agtype_parser.c: In function ‘lex_expect’:
src/backend/utils/adt/agtype_parser.c:142:9: error: implicit declaration of function ‘report_parse_error’ [-Wimplicit-function-declaration]
142 | report_parse_error(ctx, lex);
| ^~~~~~~~~~~~~~~~~~
src/backend/utils/adt/agtype_parser.c: In function ‘agtype_lex’:
src/backend/utils/adt/agtype_parser.c:633:21: error: implicit declaration of function ‘report_invalid_token’; did you mean ‘report_invalid_encoding’? [-Wimplicit-function-declaration]
633 | report_invalid_token(lex);
| ^~~~~~~~~~~~~~~~~~~~
| report_invalid_encoding
src/backend/utils/adt/agtype_parser.c: At top level:
src/backend/utils/adt/agtype_parser.c:1151:13: warning: conflicting types for ‘report_parse_error’; have ‘void(agtype_parse_context, agtype_lex_context *)’
1151 | static void report_parse_error(agtype_parse_context ctx,
| ^~~~~~~~~~~~~~~~~~
src/backend/utils/adt/agtype_parser.c:1151:13: error: static declaration of ‘report_parse_error’ follows non-static declaration
src/backend/utils/adt/agtype_parser.c:142:9: note: previous implicit declaration of ‘report_parse_error’ with type ‘void(agtype_parse_context, agtype_lex_context *)’
142 | report_parse_error(ctx, lex);
| ^~~~~~~~~~~~~~~~~~
src/backend/utils/adt/agtype_parser.c:1258:13: warning: conflicting types for ‘report_invalid_token’; have ‘void(agtype_lex_context *)’
1258 | static void report_invalid_token(agtype_lex_context *lex)
| ^~~~~~~~~~~~~~~~~~~~
src/backend/utils/adt/agtype_parser.c:1258:13: error: static declaration of ‘report_invalid_token’ follows non-static declaration
src/backend/utils/adt/agtype_parser.c:633:21: note: previous implicit declaration of ‘report_invalid_token’ with type ‘void(agtype_lex_context *)’
633 | report_invalid_token(lex);
| ^~~~~~~~~~~~~~~~~~~~
src/backend/utils/adt/agtype_parser.c:1258:13: warning: ‘report_invalid_token’ defined but not used [-Wunused-function]
1258 | static void report_invalid_token(agtype_lex_context *lex)
| ^~~~~~~~~~~~~~~~~~~~
src/backend/utils/adt/agtype_parser.c:1151:13: warning: ‘report_parse_error’ defined but not used [-Wunused-function]
1151 | static void report_parse_error(agtype_parse_context ctx,
| ^~~~~~~~~~~~~~~~~~
```

(Debian unstable amd64, gcc 15.3)

Start by reproducing the PG19 beta 2 build on Debian unstable with GCC 15.3 and inspect src/backend/utils/adt/agtype_parser.c, especially the pg_noreturn declarations and the related function definitions. Done means the extension compiles successfully without the reported declaration errors.

Written by the indexing model from the issue text.