bug#26048: Use absolute file names in NEED instead of adding many entries to RUNPATH

[Ludovic Courtès]

Hello!

As Andy just noted on IRC, shared library lookup is inefficient in Guix,
because there’s one entry per library in RUNPATH.  So we get:

--8<---------------cut here---------------start------------->8---
open("/gnu/store/y8ppqsxiki39n4mqpb4mab6bgwqsnnp7-libgc-7.4.2/lib/libm.so.6", 
O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/gnu/store/w0bkj9qh7iqcklm5ld8ghg1ynnzqyv00-libffi-3.2.1/lib/libm.so.6", 
O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/gnu/store/d5gw4i6bnyznmbr55ba39bl3pgrhsyp0-libunistring-0.9.6/lib/libm.so.6",
 O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/gnu/store/6k08nkddnrb15h5pwp1s0fa94mr1qas9-gmp-6.1.1/lib/libm.so.6", 
O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/gnu/store/9yn89bkl8vcg5rh9dmw3jijciwgrwjls-libltdl-2.4.6/lib/libm.so.6", 
O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/gnu/store/iwgi9001dmmihrjg4rqhd6pa6788prjw-glibc-2.24/lib/libm.so.6", 
O_RDONLY|O_CLOEXEC) = 3
--8<---------------cut here---------------end--------------->8---

An alternate approach would be for ld-wrapper to replace “-lfoo” with
“/gnu/store/…/libfoo.so”, which would add the absolute file name as
NEEDed in the ELF file.

Ludo’.