fix lc15 build: put src/common/libbts.a left of -losmogsm
fix lc15 build: put src/common/libbts.a left of -losmogsm

When switching to the gsm_chan_t_names string list from libosmogsm,
libosmogsm actually became a dependency of the local libbts.a.

The breaking change is in openbsc.git 29048b2a80b5865ffc41fa4401113c5826227e23
and came in here because gsm_data_shared.h is included from openbsc.

Change-Id: I70e5735fc2a212305182d46a7e8485d0199ade7b

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts