[NO_SETENV=YesPlease])
AC_SUBST(NO_SETENV)
#
+# Define NO_UNSETENV if you don't have unsetenv in the C library.
+AC_CHECK_FUNC(unsetenv,
+[NO_UNSETENV=],
+[NO_UNSETENV=YesPlease])
+AC_SUBST(NO_UNSETENV)
+#
# Define NO_MKDTEMP if you don't have mkdtemp in the C library.
AC_CHECK_FUNC(mkdtemp,
[NO_MKDTEMP=],