Fluent Bit failed to build on Debian Bookworm

## Bug Report

CFL is failed to compile Debian Bookworm.

This is the same issue which I already reported on https://github.com/fluent/cfl/pull/89.

**Describe the bug**

TIME_UTC is declared as a constant for C11 specification.

ref: https://cppreference.com/c/chrono/TIME_UTC

**To Reproduce**
- Steps to reproduce the problem:

Create a compiling environment on Debian bookworm and then execute `make`:

```
% LANG=C make
[ 1%] Built target backtrace
[ 6%] Built target c-ares
[ 6%] Built target jsmn
[ 6%] Built target sqlite3
[ 7%] Built target flb-conv
[ 7%] Built target xxhash
[ 7%] Building C object lib/cfl/src/CMakeFiles/cfl-static.dir/cfl_time.c.o
/home/cosmo/GitHub/fluent-bit/lib/cfl/src/cfl_time.c: In function 'cfl_time_now':
/home/cosmo/GitHub/fluent-bit/lib/cfl/src/cfl_time.c:55:5: warning: implicit declaration of function 'timespec_get' [-Wimplicit-function-declaration]
55 | timespec_get(&tm, TIME_UTC);
| ^~~~~~~~~~~~
/home/cosmo/GitHub/fluent-bit/lib/cfl/src/cfl_time.c:55:23: error: 'TIME_UTC' undeclared (first use in this function)
55 | timespec_get(&tm, TIME_UTC);
| ^~~~~~~~
/home/cosmo/GitHub/fluent-bit/lib/cfl/src/cfl_time.c:55:23: note: each undeclared identifier is reported only once for each function it appears in
make[2]: *** [lib/cfl/src/CMakeFiles/cfl-static.dir/build.make:118: lib/cfl/src/CMakeFiles/cfl-static.dir/cfl_time.c.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:4631: lib/cfl/src/CMakeFiles/cfl-static.dir/all] Error 2
make: *** [Makefile:166: all] Error 2
```

**Expected behavior**

Succeed to compile Debian Bookworm.

**Screenshots**

**Your Environment**

* Version used: master d55459d492c5c019c0f7dc24db42e69ef47a5437
* Configuration: Only building
* Environment name and version (e.g. Kubernetes? What version?): Debian Bookworm in Crostini (Chromebook x86_64)
* Server type and version: Client
* Operating System and version:

```
% cat /etc/*-release
PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"
NAME="Debian GNU/Linux"
VERSION_ID="12"
VERSION="12 (bookworm)"
VERSION_CODENAME=bookworm
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
```

* Filters and plugins: N/A

**Additional context**

Start by reading lib/cfl/src/cfl_time.c around cfl_time_now and reproduce the failure with make on Debian 12 Bookworm. Check how the project selects its C standard and handles timespec_get/TIME_UTC there. Done means a clean build completes on Debian Bookworm without the reported error.

Written by the indexing model from the issue text.