hammer.git: add missing scripts/Makefile.local

The dummy scripts/Makefile.local was missing, causing a build failure with
the bare hammer.git repository. Fix that.
hammer.git: brand git branches with hammer.git

Brand git branches with hammer.git instead of los.git. LOS uses HAMMER
and not vice versa.
hammer.git: define LIB_NAME

Provide a default LIB_NAME=lib for build scripts, which is the library
directory name where primary ABI libraries are located.