The only reason to use int instead of the enum was the lack of header
iu_client.h when not building with Iu support. Rather use the configure result
properly, include the header when Iu support is built and use the proper enum.
Omit the entire iu sub-struct when building without Iu.
Add LIBOSMORANAP_CFLAGS to libvlr, in order to find the iu_client.h header (now
also included from gsm_data.h).
Rationale: Instead of using a questionable typecast from int* to enum*, we can
now use the enum member directly without needing to silence compiler warnings.
Change-Id: Ic9f8bf53f4b605c166e84cd7edd90c10fe7d7a1f
21adb2bcd1