Fix issue raised by Stefan Friedel: remove an extraneous -L that is

added by hwloc's embedding so that it doesn't appear in
libhwloc_embedded.la (and therefore propogate all the way up to
libmpi.la). 

Committed upstream in hwloc SVN r5588.

This commit was SVN r28457.

The following SVN revisions from the original message are invalid or
inconsistent and therefore were not cross-referenced:
  r5588

opal/mca/hwloc/hwloc152/hwloc/config/hwloc.m4

@@ -762,7 +762,6 @@ EOF])
     AC_SUBST(HWLOC_CFLAGS)
     HWLOC_CPPFLAGS='-I$(HWLOC_top_builddir)/include -I$(HWLOC_top_srcdir)/include'
     AC_SUBST(HWLOC_CPPFLAGS)
-    HWLOC_LDFLAGS='-L$(HWLOC_top_builddir)/src'
     AC_SUBST(HWLOC_LDFLAGS)
     AC_SUBST(HWLOC_LIBS)