libmaxminddb: fixup lib and include dirs in pkg-config

libmaxminddb: fixup lib and include dirs in pkg-config

libmaxminddb has switched to using CMAKE_INSTALL_PREFIX,
CMAKE_INSTALL_LIBDIR and CMAKE_INSTALL_INCLUDEDIR for generating the
pkg-config in upstream commit [1] and thus broke pkg-config file
generation in openwrt.

It would generate:
prefix=/usr
exec_prefix=/usr
libdir=lib
includedir=include

Obviously libdir and includedirs are incorrect for OpenWrt and this
would then cause pdns compilation to fail if geoip backend was enabled
since it uses pkg-config to get the required flags and passing just
lib for LDFLAGS would cause libtool to error out since that path is not
valid.

So, lets use SED magic to replace libdir and includedir with the correct
paths, so now pkg-config looks like:
prefix=/usr
exec_prefix=/usr
libdir=${exec_prefix}/lib
includedir=${prefix}/include

[1] https://github.com/maxmind/libmaxminddb/commit/8b4bf0dec99bc248c36e49e0837efb749e7d46f6

Fixes: 9f7357880f64 ("libmaxminddb: update to 1.11.0")
Signed-off-by: Robert Marko <robimarko@gmail.com>