Move wchar.c and encnames.c to src/common/.

Formerly, various frontend directories symlinked these two sources
and then built them locally.  That's an ancient, ugly hack, and
we now have a much better way: put them into libpgcommon.
So do that.  (The immediate motivation for this is the prospect
of having to introduce still more symlinking if we don't.)

This commit moves these two files absolutely verbatim, for ease of
reviewing the git history.  There's some follow-on work to be done
that will modify them a bit.

Robert Haas, Tom Lane

Discussion: https://postgr.es/m/CA+TgmoYO8oq-iy8E02rD8eX25T-9SmyxKWqqks5OMHxKvGXpXQ@mail.gmail.com

src/interfaces/libpq/.gitignore

@@ -1,4 +1 @@
 /exports.list
-# .c files that are symlinked in from elsewhere
-/encnames.c
-/wchar.c

src/interfaces/libpq/Makefile

@@ -45,11 +45,6 @@ OBJS = \
 	pqexpbuffer.o \
 	fe-auth.o
 
-# src/backend/utils/mb
-OBJS += \
-	encnames.o \
-	wchar.o
-
 ifeq ($(with_openssl),yes)
 OBJS += \
 	fe-secure-common.o \
@@ -102,17 +97,7 @@ include $(top_srcdir)/src/Makefile.shlib
 backend_src = $(top_srcdir)/src/backend
 
 
-# We use a few backend modules verbatim, but since we need
-# to compile with appropriate options to build a shared lib, we can't
-# use the same object files built for the backend.
-# Instead, symlink the source files in here and build our own object files.
-# When you add a file here, remember to add it in the "clean" target below.
-
-encnames.c wchar.c: % : $(backend_src)/utils/mb/%
-	rm -f $@ && $(LN_S) $< .
-
-
-# Make dependencies on pg_config_paths.h visible, too.
+# Make dependencies on pg_config_paths.h visible in all builds.
 fe-connect.o: fe-connect.c $(top_builddir)/src/port/pg_config_paths.h
 fe-misc.o: fe-misc.c $(top_builddir)/src/port/pg_config_paths.h
 
@@ -144,8 +129,6 @@ clean distclean: clean-lib
 	rm -f $(OBJS) pthread.h
 # Might be left over from a Win32 client-only build
 	rm -f pg_config_paths.h
-# Remove files we (may have) symlinked in from other places
-	rm -f encnames.c wchar.c
 
 maintainer-clean: distclean
 	$(MAKE) -C test $@