pkg-config file is broken when CMAKE_INSTALL_{INCLUDE,LIB}DIR is absolute

[alexshpilkin]

As per title: src/wildmidi.pc.in has

prefix=@CMAKE_INSTALL_PREFIX@
exec_prefix=${prefix}
libdir=${exec_prefix}/@CMAKE_INSTALL_LIBDIR@
includedir=${exec_prefix}/@CMAKE_INSTALL_INCLUDEDIR@

and so can’t handle absolute paths in CMAKE_INSTALL_{INCLUDE,LIB}DIR. This leads to a broken .pc file on NixOS in particular.

Similar to open-source-parsers/jsoncpp#1199. See “Concatenating paths when building pkg-config files” for a discussion of the problem and a suggested fix (I don’t know CMake myself, sorry).

[sezero]

This should be fixed by c4a6330: can you confirm?

If it's not fixed, or if there are further issues, please drop a note here.