Description: The arpackSolver.pc file installed with 'arpack' depends on 'eigen3', but no eigen3.pc file is installed by arpack, nor by any of its dependencies.

This is relevant whenever one wants to depend on arpack via pkg-config.
It bites me specifically because a tool I use reads in the entire pkg-config database, which fails when any package within it is broken (like arpackSolver.pc is).


Additional info:
* arpack 3.9.0-2


Steps to reproduce:

```
~$ pacman -Qo /usr/lib/pkgconfig/arpackSolver.pc
/usr/lib/pkgconfig/arpackSolver.pc is owned by arpack 3.9.0-2

~$ cat /usr/lib/pkgconfig/arpackSolver.pc
prefix=/usr
exec_prefix=${prefix}
includedir=${prefix}/include/arpack-ng

Name: arpackSolver
Description: Utility to test arpack with matrix market files
Version: 3.9.0
URL: https://github.com/opencollab/arpack-ng/
Requires: arpack, eigen3 >= 3.3
Cflags: -I${includedir}

~$ pkg-config --modversion arpackSolver
Package eigen3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `eigen3.pc'
to the PKG_CONFIG_PATH environment variable
Package 'eigen3', required by 'arpackSolver', not found

(1) ~$ pkg-config --modversion eigen3
Package eigen3 was not found in the pkg-config search path.
Perhaps you should add the directory containing `eigen3.pc'
to the PKG_CONFIG_PATH environment variable
Package 'eigen3', required by 'virtual:world', not found

(1) ~$ pacman -Ql $(pactree arpack -u) | grep -F .pc | cut -d' ' -f2- | sort -u | grep eigen

(1) ~$ pacman -Ql $(pactree arpack -u) | grep -F .pc | cut -d' ' -f2- | sort -u | xargs grep eigen
/usr/lib/pkgconfig/arpack.pc:Description: Collection of Fortran77 subroutines designed to solve large scale eigenvalue problems
/usr/lib/pkgconfig/arpackSolver.pc:Requires: arpack, eigen3 >= 3.3
/usr/lib/pkgconfig/parpack.pc:Description: Collection of Fortran77 subroutines designed to solve large scale eigenvalue problems

~$
```

The last two commands show that none of the transitive dependencies of 'arpack' include a file with the string "eigen" in the name, nor in their contents.