configure: require libgsm for --enable-mgcp-transcoding

Fail in configure if libgsm is not found.

Before this, the --enable-mgcp-transcoding would gladly accept that libgsm is
missing and the build would fail later because of missing linking and undefined
references.

Change-Id: Ic23157cc5b75694f400a176c31f97d71e861ea02
1 file changed
tree: 46f857f982fe53d2a82462f7cdfbe55ea967da8c
  1. contrib/
  2. debian/
  3. openbsc/
  4. .gitignore
  5. .gitreview