build: Run tr only once in configure.ac.

build: Run tr only once in configure.ac.

The configure script creates the subsystem error enums for config.h
from the list of object file names by turning the base name into
upper case and prepending "SS_". For the conversion to upper case we
currently execute the tr command once for each object.

This patch changes the corresponding shell code of configure.ac to
first build the full enum and then turn all words into upper case
in one go. This way tr is only executed once which should save us a
few cycles.