gh-90005: Don't link with libbsd if not needed (#105236)

The regression was introduced with commit 5b946ca.
Restore pre gh-29696 behaviour.

Author: erlend-aasland

Misc/NEWS.d/next/Build/2023-06-06-09-08-10.gh-issue-90005.8mmeJQ.rst

@@ -0,0 +1 @@
+Fix a regression in :file:`configure` where we could end up unintentionally linking with ``libbsd``.

configure

@@ -4908,9 +4908,8 @@ AC_CACHE_CHECK([for flock declaration], [ac_cv_flock_decl],
 ])
 dnl Linking with libbsd may be necessary on AIX for flock function.
 AS_VAR_IF([ac_cv_flock_decl], [yes],
-  AC_CHECK_FUNCS([flock])
-  AC_CHECK_LIB([bsd], [flock], [FCNTL_LIBS="-lbsd"])
-)
+  [AC_CHECK_FUNCS([flock], [],
+    [AC_CHECK_LIB([bsd], [flock], [FCNTL_LIBS="-lbsd"])])])
 
 PY_CHECK_FUNC([getpagesize], [#include <unistd.h>])