Description of problem:

XDG_CACHE_HOME=/var/cache/user/root
# ls /var/cache/user/root
ls: cannot access '/var/cache/user/root': No such file or directory

Program received signal SIGABRT, Aborted.
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:58
58      }
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:58
#1  0x00007ffff630756a in __GI_abort () at abort.c:89
#2  0x000055555555bf28 in package::extracted_packages_parent_dir[abi:cxx11]() ()
    at abipkgdiff.cc:574
#3  0x0000555555561887 in package::package (this=0x55555577d010,
    path="/data/repos/fedora/development/rawhide/Everything/x86_64/os/Packages/f/fftw-libs-double-3.3.4-7.fc24.x86_64.rpm", dir="package1", pkg_kind=package::KIND_MAIN) at abipkgdiff.cc:314
#4  0x000055555555935e in main (argc=<optimized out>, argv=<optimized out>)
    at abipkgdiff.cc:2003
(gdb) up
#1  0x00007ffff630756a in __GI_abort () at abort.c:89
89            raise (SIGABRT);
(gdb) up
#2  0x000055555555bf28 in package::extracted_packages_parent_dir[abi:cxx11]() ()
    at abipkgdiff.cc:574
574             abort();
(gdb) list
569
570           string libabigail_tmp_dir_template = p;
571           libabigail_tmp_dir_template += "/abipkgdiff-tmp-dir-XXXXXX";
572
573           if (!mkdtemp(const_cast<char*>(libabigail_tmp_dir_template.c_str())))
574             abort();
575
576           p = libabigail_tmp_dir_template;
577         }
578
(gdb) print libabigail_tmp_dir_template
$1 = "/var/cache/user/root/abipkgdiff-tmp-dir-35vxEo"

Version-Release number of selected component (if applicable):
libabigail-1.0-0.8.rc5.5.fc26.x86_64

It's hard to tell from https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html but if the directory doesn't exist I believe programs should create it with 0700 permissions.