Use a stub replacement and disable dss when sbrk is not supported

configure.ac

@@ -678,6 +678,14 @@ fi
 ],
 [enable_dss="0"]
 )
+dnl Check whether the BSD/SUSv1 sbrk() exists.  If not, disable DSS support.
+AC_CHECK_FUNC([sbrk], [have_sbrk="1"], [have_sbrk="0"])
+if test "x$have_sbrk" = "x1" ; then
+  AC_DEFINE([JEMALLOC_HAVE_SBRK], [ ])
+else
+  enable_dss="0"
+fi
+
 if test "x$enable_dss" = "x1" ; then
   AC_DEFINE([JEMALLOC_DSS], [ ])
 fi

include/jemalloc/jemalloc_defs.h.in

@@ -108,6 +108,9 @@
 #  define JEMALLOC_ATTR(s) JEMALLOC_CATTR(s,)
 #endif
 
+/* Defined if sbrk() is supported. */
+#undef JEMALLOC_HAVE_SBRK
+
 /* Non-empty if the tls_model attribute is supported. */
 #undef JEMALLOC_TLS_MODEL
 

src/chunk_dss.c

@@ -3,6 +3,17 @@
 /******************************************************************************/
 /* Data. */
 
+#ifndef JEMALLOC_HAVE_SBRK
+void *
+sbrk(intptr_t increment)
+{
+
+	not_implemented();
+
+	return (NULL);
+}
+#endif
+
 /*
  * Protects sbrk() calls.  This avoids malloc races among threads, though it
  * does not protect against races with threads that call sbrk() directly.