package/flatbuffers: fix locale independent on musl

package/flatbuffers: fix locale independent on musl

Fix locale indepdendent which is enabled on musl since version 1.11.0
and
https://github.com/google/flatbuffers/commit/5f32f948102e65eaeea461b44f3b43f96c7a7a5a
resulting in the following build failure on snort3 since bump to version
3.1.6 in commit	e66f2fd310374779d415fa683813cc5f5ccf6be9:

In file included from /tmp/instance-0/output-1/host/x86_64-buildroot-linux-musl/sysroot/usr/include/flatbuffers/flexbuffers.h:24,
                 from /tmp/instance-0/output-1/host/x86_64-buildroot-linux-musl/sysroot/usr/include/flatbuffers/idl.h:26,
                 from /tmp/instance-0/output-1/build/snort3-3.1.6.0/src/network_inspectors/perf_monitor/fbs_formatter.cc:29:
/tmp/instance-0/output-1/host/x86_64-buildroot-linux-musl/sysroot/usr/include/flatbuffers/util.h: In function 'void flatbuffers::strtoval_impl(int64_t*, const char*, char**, int)':
/tmp/instance-0/output-1/host/x86_64-buildroot-linux-musl/sysroot/usr/include/flatbuffers/util.h:258:12: error: 'strtoll_l' was not declared in this scope; did you mean 'strcoll_l'?
  258 |     *val = __strtoll_impl(str, endptr, base);
      |            ^~~~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/68045b83e94f8caa337b1af7ed5f493ac1a55c47

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>