on finding some GNU libraries under /usr/local rather than /usr: interference between .la files?

[Marco Maggi]

Ciao,

  while building  and installing the  latest release of  some GNU
package on a x86_64-unknown-linux-gnu, Slackware 14.0, I stumbled
on this problem:

* Slackware packages  install libraries under  "/usr/lib64"; they
  come with .la files.

* My custom  installations put libraries  under "/usr/local/lib";
  .la files are installed with me doing nothing to them.

* Some custom  installations of  packages making  use of  the GNU
  Autotools  like  the  stack   GMP,  MPFR,  MPC  correctly  find
  installed libraries under "/usr/local/lib"; so I see:

     $ ldd /usr/local/lib/libmpfr.so|grep gmp
     libgmp.so.10 => /usr/local/lib/libgmp.so.10 (0x00007fc545c32000)

     $ ldd /usr/local/lib/libmpc.so|grep '\(gmp\|mpfr\)'
     libmpfr.so.4 => /usr/local/lib/libmpfr.so.4 (0x00007f21524fa000)
     libgmp.so.10 => /usr/local/lib/libgmp.so.10 (0x00007f2152281000)

* Some  GNU packages,  a subset  of  which is  also installed  by
  Slackware, fail to find libraries under "/usr/local": they find
  libraries under "/usr/lib64".

  It appears that  the problem is some interference  from the .la
files  installed under  "/usr/lib64": if  I (temporarily)  remove
*all*  of them  the installations  succeed; I  am unable  to find
which ones among the Slackware's .la files cause troubles.

  The full inspection of the problem  for Gnutls is in the thread
"[gnutls-help]  on finding  nettle under  /usr/local rather  than
under /usr (GNU+Linux 64-bit system)" at:

<http://lists.gnutls.org/pipermail/gnutls-help/2013-May/003136.html>

TIA
-- 
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