[tom@trueos-7040] ~% pkg-config --variable pcfiledir gtk+-2.0
/usr/local/libdata/pkgconfig
[tom@trueos-7040] ~% pkg-config --variable pcfiledir fontconfig
/usr/local/libdata/pkgconfig
[tom@trueos-7040] ~% cat "$(pkg-config --variable pcfiledir fontconfig)/fontconfig.pc"
Illegal variable name.
[tom@trueos-7040] ~% 

[tom@trueos-7040] ~% locate fontconfig
/usr/local/include/fontconfig
/usr/local/include/fontconfig/fcfreetype.h
/usr/local/include/fontconfig/fcprivate.h
/usr/local/include/fontconfig/fontconfig.h
/usr/local/include/qt5/QtPlatformSupport/5.6.2/QtPlatformSupport/private/qfontconfigdatabase_p.h
/usr/local/include/qt5/QtPlatformSupport/5.6.2/QtPlatformSupport/private/qfontenginemultifontconfig_p.h
/usr/local/lib/girepository-1.0/fontconfig-2.0.typelib
/usr/local/lib/libfontconfig.a
/usr/local/lib/libfontconfig.so
/usr/local/lib/libfontconfig.so.1
/usr/local/lib/libfontconfig.so.1.9.2
/usr/local/libdata/pkgconfig/fontconfig.pc
/usr/local/pkg-cache/fontconfig-2.12.1,1-581b37418c.txz
/usr/local/pkg-cache/fontconfig-2.12.1,1.txz
/usr/local/share/doc/fontconfig
/usr/local/share/doc/fontconfig/fontconfig-user.html
/usr/local/share/doc/fontconfig/fontconfig-user.pdf
/usr/local/share/doc/fontconfig/fontconfig-user.txt
/usr/local/share/gir-1.0/fontconfig-2.0.gir
/usr/local/share/licenses/fontconfig-2.12.1,1
/usr/local/share/licenses/fontconfig-2.12.1,1/catalog.mk
/usr/local/share/licenses/fontconfig-2.12.1,1/LICENSE
/usr/local/share/licenses/fontconfig-2.12.1,1/MIT
/var/db/fontconfig
/var/db/fontconfig/1fe06f2352c4cb897117a756a050a9d4-le64.cache-7
/var/db/fontconfig/317e92aa1a4d3e601fb38e2d3c7b366a-le64.cache-7
/var/db/fontconfig/4c599c202bc5c08e2d34565a40eac3b2-le64.cache-7
/var/db/fontconfig/5590eef8711d78f75a1d19f78ae9af8f-le64.cache-7
/var/db/fontconfig/830bb1cbfd3d582459af9eb69ef1dd53-le64.cache-7
/var/db/fontconfig/b505adbf72d7253408dd67084a8aa967-le64.cache-7
/var/db/fontconfig/ba1d92d9e40780c65c2952558e6fa6f5-le64.cache-7
/var/db/fontconfig/bd930d03fc0401d0f1dcfa7b9bdc1687-le64.cache-7
/var/db/fontconfig/CACHEDIR.TAG
/var/db/fontconfig/d3b21a501470a17bfd0b9b6aedc735bd-le64.cache-7                                                                                           
/var/db/fontconfig/ece4193fc5c4a4effb1dc60970b2e31e-le64.cache-7