Always use Linux version of test_coding_rules

Because only Linux version of this tool is fully functional (while the
MSW one just exits with an error), always use it, even in the build
targeting MSW.

This is enough to make concinnity checks to work in any build.

GNUmakefile

@@ -431,12 +431,23 @@ uninstall:
 
 # Custom tools built from source.
 
-TEST_CODING_RULES := $(build_dir)/test_coding_rules$(EXEEXT)
+# Always build host (i.e. Linux) version of this tool, as it depends on PCRE
+# library only available on POSIX systems and it is preferable to run it on
+# the host, rather than the target, system in any case.
+#
+# Note that this implies that the tool binary doesn't need to use EXEEXT and
+# that PERFORM should _not_ be used when running it.
+host_triplet     := x86_64-pc-linux-gnu
+host_exec_prefix := $(prefix)/$(LMI_COMPILER)_$(host_triplet)
+host_build_dir   := $(host_exec_prefix)/build/$(build_type)
+host_localbindir := $(prefix)/local/$(LMI_COMPILER)_$(host_triplet)/bin
+
+TEST_CODING_RULES := $(host_build_dir)/test_coding_rules
 
 .PHONY: custom_tools
 custom_tools:
-	@$(MAKE) test_coding_rules$(EXEEXT)
-	@$(INSTALL) -c -m 0775 $(TEST_CODING_RULES) $(localbindir)
+	@$(MAKE) LMI_TRIPLET=$(host_triplet) test_coding_rules
+	@$(INSTALL) -c -m 0775 $(TEST_CODING_RULES) $(host_localbindir)
 
 ################################################################################
 
@@ -501,7 +512,7 @@ check_concinnity: source_clean custom_tools
 	      || $(ECHO) "... in file $$z"; \
 	  done;
 	@$(ECHO) "  Miscellaneous problems:"
-	@cd $(prefascicle_dir) && $(PERFORM) $(TEST_CODING_RULES) *
+	@cd $(prefascicle_dir) && $(TEST_CODING_RULES) *
 
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