Most pkgconfig files contain a Libs: variable, which is either /usr/lib
or /usr/lib64. If a 32bit and a 64bit variant of fmt libraries is
installed, the last one wins. As a result compiling for the other
bitsize will fail.

Instead of sharedir use libdir as install target.

Fixes commit 9d0c9c4b
Fixes commit 287342daSigned-off-by: Olaf Hering <olaf@aepfle.de>

* Added missing typename to FMT_STRING.

This is so that FMT_STRING can be used in a template.

This is similar to https://github.com/apple/swift/blob/master/CONTRIBUTING.md
with an explicit clause that allows changing license for #1073.