If the original prefix setting is empty, skip prepending the redefined
prefix to other variables. This works the same as if the pc file doesn't
have a prefix variable at all.
https://bugs.freedesktop.org/show_bug.cgi?id=97453-empty
Wine outputs the paths with carriage returns, which later breaks
commands they're used in. Hopefully this doesn't break the msys case,
but I think it should be safe enough. Really this needs general handling
of Windows paths instead of ad hoc fixes, but that's for another day.
https://bugs.freedesktop.org/show_bug.cgi?id=66939
When pkg-config redefines the .pc file's prefix variable, it will be in
the platform's native format. Convert the expected results as
necessary. This only affects the relocatable test because it explicitly
sets --define-prefix or uses .pc files in a pkgconfig/ directory. Other
tests do not have their prefixes redefined for this reason.
Exercise the ${pcfiledir} and --define-prefix features for allowing
relocation of packages. The --define-prefix test .pc files are put in a
pkgconfig subdirectory since the feature will only be enabled in that
situation.
