Fix symlink updates when switching configurations

Use all-local hook to ensure lsdiff and grepdiff symlinks are built
during 'make', so they correctly point to filterdiff or patchfilter
depending on the configuration.

Previously, after reconfiguring between implementations, running 'make'
would not update the symlinks, leaving them pointing to the wrong target.

Also ensure the patchview directory exists before creating symlinks in it,
which fixes 'make distcheck'.

Assisted-by: Claude Code

Author: twaugh

Makefile.am

@@ -5,8 +5,6 @@ DISTCLEANFILES = src/stamp-h[0-9]* src/config.h
 
 bin_PROGRAMS = src/interdiff src/filterdiff src/rediff
 
-# lsdiff is provided by symlink to filterdiff (unless scanner-patchfilter is enabled)
-
 # Scanner-based unified patchfilter tool (experimental)
 if USE_SCANNER_PATCHFILTER
 bin_PROGRAMS += src/patchfilter
@@ -152,6 +150,11 @@ $(filterdiff_links): src/filterdiff$(EXEEXT)
 $(patchview_links): patchview/patchview-wrapper$(EXEEXT)
 	ln -sf $(notdir $<) $@
 
+# Ensure all symlinks are created during build
+all-local: $(interdiff_links) $(filterdiff_links) src/lsdiff$(EXEEXT) src/grepdiff$(EXEEXT)
+	@test -d patchview || mkdir -p patchview
+	@$(MAKE) $(AM_MAKEFLAGS) $(patchview_links)
+
 install-exec-hook:
 	@for f in $(interdiff_links); do \
 	    ln -sf "`echo interdiff$(EXEEXT) | sed '$(transform)'`" \