As someone had pointed out, I was using a gnu sed when modifying the make file for libgsm.
MacOSX does not ship with a gnu sed.
This is how I usually build gnu utilities (and basically, everything else I need and build from source)
As an example, how to build sed is shown:
First, obtain and unpack sed
$ /usr/bin/curl -O ftp://ftp.gnu.org/pub/gnu/sed/sed-4.1.5.tar.gz $ tar xzpf sed-4.1.5
Set up compiler flags
$ export CFLAGS="-isysroot /Developer/SDKs/MacOSX10.4u.sdk -arch x86_64 -arch ppc64 -arch ppc -arch i386 -arch x86_64 -mmacosx-version-min=10.4" $ export LDFLAGS="-Wl,-syslibroot,/Developer/SDKs/MacOSX10.4u.sdk -arch x86_64 -arch ppc64 -arch ppc -arch i386 -mmacosx-version-min=10.4"
Start the compilation and install