Protect the headers

This commit was SVN r8448.

ompi/mca/allocator/base/allocator_base_open.c

@@ -19,7 +19,9 @@
 
 #include "ompi_config.h"
 #include <stdio.h>
+#ifdef HAVE_STRING_H
 #include <string.h>
+#endif  /* HAVE_STRING_H */
 
 #include "mca/mca.h"
 #include "mca/base/base.h"

ompi/mca/mpool/base/mpool_base_open.c

@@ -25,8 +25,9 @@
 #include "mca/mpool/mpool.h"
 #include "mca/mpool/base/base.h"
 #include "ompi/include/constants.h"
+#ifdef HAVE_UNISTD_H
 #include <unistd.h> 
-
+#endif  /* HAVE_UNISTD_H */
 
 /*
  * The following file was created by configure.  It contains extern