System library paths?

[Hauke Fath <hf%spg.tu-darmstadt.de@localhost>]

All,

I have a small pkgsrc installation on Arch Linux for packages they
don't provide. Running a pkg-rolling-replace today, I saw graphics/tiff
break with

[...]
+ /opt/local/bin/nbmake all
/opt/local/bin/nbmake  all-am
/bin/sh ../libtool  --tag=CXX    --mode=link c++   -O2
  -D_FORTIFY_SOURCE=2 -I/opt/local/include -no-undefined -version-info
  8:0:3   -L/opt/local/lib -Wl,-R/opt/local/lib -o libtiffxx.la
  -rpath /opt/local/lib
  tif_stream.lo ../libtiff/libtiff.la ../port/libport.la -llzma -ljbig
  -ljpeg -lz -lm
+ /bin/sh ../libtool --tag=CXX --mode=link c++ -O2 -D_FORTIFY_SOURCE=2
  -I/opt/local/include -no-undefined -version-info 8:0:3
  -L/opt/local/lib -Wl,-R/opt/local/lib -o libtiffxx.la
  -rpath /opt/local/lib
  tif_stream.lo ../libtiff/libtiff.la ../port/libport.la -llzma -ljbig
  -ljpeg -lz -lm libtool: link: c++  -fPIC -DPIC -shared
  -nostdlib /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/../../../../lib/crti.o /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/crtbeginS.o  .libs/tif_stream.o
  -Wl,--whole-archive ../port/.libs/libport.a -Wl,--no-whole-archive
  -Wl,-rpath
  -Wl,/var/obj/pkgsrc/graphics/tiff/work/tiff-4.0.9/libtiff/.libs
  -Wl,-rpath -Wl,/var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib
  -Wl,-rpath -Wl,/opt/local/lib -Wl,-rpath
  -Wl,/var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib
  -L/var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib ../libtiff/.libs/libtiff.so /var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib/liblzma.so
  -lpthread
  -lrt /var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib/libjbig.so /var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib/libjpeg.so /var/obj/pkgsrc/graphics/tiff/work/.buildlink/lib/libz.so
  -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0
  -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/../../../../lib
  -L/lib/../lib -L/usr/lib/../lib
  -L/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/../../.. -lstdc++ -lm -lc
  -lgcc_s /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/crtendS.o /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/../../../../lib/crtn.o
  -O2 -Wl,-rpath -Wl,/opt/local/lib   -pthread -Wl,-soname
  -Wl,libtiffxx.so.5 -o .libs/libtiffxx.so.5.3.0 g++:
  error: /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/../../../../lib/crti.o:
  No such file or directory g++:
  error: /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/crtbeginS.o: No such
  file or directory g++:
  error: /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/crtendS.o: No such file
  or directory g++:
  error: /usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/../../../../lib/crtn.o:
  No such file or directory *** Error code 1
[...]

where

% ls -l /usr/lib/gcc/x86_64-pc-linux-gnu/
total 8
drwxr-xr-x 7 root root 4096 Nov 22 14:17 5.5.0
drwxr-xr-x 8 root root 4096 Jan 16 17:36 7.2.1
%

osabi-Linux-4.14.13 has been rebuilt, and I manually rebuilt cwrappers,
but to no avail.

My question: What is responsible for setting the versioned path
"/usr/lib/gcc/x86_64-pc-linux-gnu/7.2.0/"?

Cheerio,
hauke