external/openldap: Don't use pthread_get/setconcurrency without declarations

At least with glibc on Linux, those two functions are only declared in
<pthread.h> when _XOPEN_SOURCE is defined.  And with
<https://github.com/llvm/llvm-project/commit/7d644e1215b376ec5e915df9ea2eeb56e2d94626>
"[C11/C2x] Change the behavior of the implicit function declaration warning" in
Clang 15 trunk that now causes hard errors

> thr_posix.c:93:9: error: call to undeclared function 'pthread_setconcurrency'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>         return pthread_setconcurrency( n );
>                ^
> thr_posix.c:107:9: error: call to undeclared function 'pthread_getconcurrency'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>         return pthread_getconcurrency();
>                ^

(vs. just silently ignored warnings) when building ExternalProject_openldap.
(And the way the corresponding AC_CHECK_FUNCS in
workdir/UnpackedTarball/openldap/configure.in works, it always set
HAVE_PTHREAD_GET/SETCONCURRENCY because it effectively checks for availability
of the symbols in a library, not for declarations of the C functions in an
include file.)

But if we explicitly define _XOPEN_SOURCE, we now also need to explicitly define
_DEFAULT_SOURCE or _BSD_SOURCE (which is otherwise implicitly defined by default
in glibc's features.h if no other such macros are defined).

Change-Id: I148d50c82ee2efc2a54f2cf4f84dead3941a3568
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133312
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions