./configure replaces @libdir@ in libcyrus_min.pc.in and libcyrus_sieve.pc.in by default with ${exec_prefix}, but ${exec_prefix} is not replaced under @exec_prefix@, as the latter is missing. So ${exec_prefix} is left undefined.
Include in libcyrus_min.pc.in and libcyrus_sieve.pc.in the line
exec_prefix = @exec_prefix@
./configure replaces @libdir@ in libcyrus_min.pc.in and libcyrus_sieve.pc.in by default with ${exec_prefix}, but ${exec_prefix} is not replaced under @exec_prefix@, as the latter is missing. So ${exec_prefix} is left undefined.
Include in libcyrus_min.pc.in and libcyrus_sieve.pc.in the line
exec_prefix = @exec_prefix@