In some cases the CMAKE_INSTAL_{BIN,MAN,DOC,LIB,INCLUDE}DIR variables
may turn out to be absolute paths in which case prepending ${prefix} in
the pkg-config .pc files will result in incorrect values.
For .pc file generation, figure out if these variables are absolute and
omit the prefix in the configured file when so.
See: ab25e4b7ed
allows for the usage of $(pkgconf --static --cflags libopenjp2) to produce
the proper CFLAGS for static linking. Relies on pkgconf rather than pkg-config
Thomas Bracht Laumann Jespersen
Andreas Sturmlechner
Biswapriyo Nath
Mathieu Malaterre
Mickael Savinaud