Add re-entrant qsort detection

Author: mattjala

config/ConfigureChecks.cmake

@@ -443,6 +443,15 @@ CHECK_FUNCTION_EXISTS (asprintf          ${HDF_PREFIX}_HAVE_ASPRINTF)
 CHECK_FUNCTION_EXISTS (vasprintf         ${HDF_PREFIX}_HAVE_VASPRINTF)
 CHECK_FUNCTION_EXISTS (waitpid           ${HDF_PREFIX}_HAVE_WAITPID)
 
+# Check for reentrant qsort variants (qsort_r on Unix/BSD, qsort_s on Windows)
+# Note: qsort_r has different signatures on GNU/Linux vs BSD/macOS, but we just
+# check for existence here. Signature differences will be handled in the code.
+CHECK_FUNCTION_EXISTS (qsort_r _HAVE_QSORT_R_TMP)
+CHECK_FUNCTION_EXISTS (qsort_s _HAVE_QSORT_S_TMP)
+if (_HAVE_QSORT_R_TMP OR _HAVE_QSORT_S_TMP)
+  set (${HDF_PREFIX}_HAVE_QSORT_REENTRANT 1)
+endif ()
+
 #-----------------------------------------------------------------------------
 # sigsetjmp is special; may actually be a macro
 #-----------------------------------------------------------------------------

src/H5pubconf.h.in

@@ -258,6 +258,9 @@
 /* Define to 1 if you have the <pwd.h> header file. */
 #cmakedefine H5_HAVE_PWD_H @H5_HAVE_PWD_H@
 
+/* Define to 1 if you have a reentrant qsort function (qsort_r or qsort_s). */
+#cmakedefine H5_HAVE_QSORT_REENTRANT @H5_HAVE_QSORT_REENTRANT@
+
 /* Define whether the Read-Only S3 virtual file driver (VFD) should be
    compiled */
 #cmakedefine H5_HAVE_ROS3_VFD @H5_HAVE_ROS3_VFD@