build: fix stale soname symlink after a library version bump

When a shared library's soname is bumped (e.g. liblinuxcncini.so.0 ->
.so.1), incremental trees keep the old .so.0 on disk. The generic
../lib/%.so symlink has two pattern rules in src/Makefile (matching
%.so.0 and %.so.1, .so.0 listed first), so make repoints the dev symlink
at the stale .so.0. Everything then links against the old library and
fails with undefined symbols (e.g. IniFile::mapLinearUnits), breaking the
python module, linuxcnc_check_ini and startup. Clean builds are immune,
so CI never sees it; only incremental builders across the bump are hit.
make clean did not help either: .so.0 is no longer in TARGETS, so
rm -f $(TARGETS) leaves it behind.

Fixes:
- liblinuxcncini.so.1 rule removes any leftover .so.[0-9]* sibling.
- Add an explicit liblinuxcncini.so -> .so.1 symlink rule. Explicit rules
  override the ambiguous pattern pair, so the symlink repoints to the
  current soname in a single build pass (the rm alone self-heals only on
  a second make).
- genclean also removes ../lib/*.so.[0-9]* so stale versioned libraries
  no longer survive make clean.

Author: grandixximo

src/Makefile

@@ -534,6 +534,7 @@ genclean:
 	find . -name '*.o' |xargs rm -f
 	-rm -rf objects
 	-rm -f $(TARGETS)
+	-rm -f ../lib/*.so.[0-9]*
 	-rm -f $(GENERATED_MANPAGES)
 	-rm -f ../rtlib/*.$(MODULE_EXT)
 	-rm -f hal/components/conv_*.comp

src/emc/ini/Submakefile

@@ -19,9 +19,16 @@ $(patsubst ./emc/ini/%,../include/%,$(LIBLCNCINICXINCS)): ../include/%.hh: ./emc
 ../lib/liblinuxcncini.so.1: $(call TOOBJS,$(LIBLCNCINISRCS))
 	$(ECHO) Creating shared library $(notdir $@)
 	@mkdir -p ../lib
-	@rm -f $@
+	@rm -f $(basename $@).[0-9]*
 	$(Q)$(CXX) $(LDFLAGS) -Wl,-soname,$(notdir $@) -shared -o $@ $^ -lfmt
 
+# Explicit symlink rule: the generic ../lib/%.so pattern rules in src/Makefile
+# match both %.so.0 and %.so.1, and the %.so.0 rule wins when a stale .so.0 is
+# left over from before this library's soname bump. Bind the dev symlink to the
+# current soname explicitly so it always repoints in a single build pass.
+../lib/liblinuxcncini.so: ../lib/liblinuxcncini.so.1
+	ln -sf $(notdir $<) $@
+
 # Command-line utility for reading ini-files
 INIVALUESRCS := emc/ini/inivalue.cc
 USERSRCS += $(INIVALUESRCS)