knot's configure script tries to detect liblmdb.so and lmdb.h, if it
can't find them it automatically adds /usr/local/{include,lib}
to the search paths then rechecks. This works well on clang archs. On
gcc archs ports-gcc automatically adds /usr/local/lib to the ld(1)
search path so detection of liblmdb.so works out of the box, but lmdb.h
can't be found since /usr/local/include hasn't been added to CPPFLAGS,
triggering a fatal error. sigh
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