build: have `make clean` clear out cmake files

Makefile.am

@@ -1,3 +1,14 @@
 ACLOCAL_AMFLAGS = -I m4
 SUBDIRS = src config tests
 EXTRA_DIST = test docs examples windows VMS cmake netware bootstrap.sh CMakeLists.txt CONTRIBUTORS README.md
+
+clean-local:
+	find -maxdepth 3 \
+		'(' \
+			-name CMakeCache.txt -o \
+			-name CMakeFiles -o \
+			-name CTestTestfile.cmake -o \
+			-name cmake_install.cmake \
+		')' \
+		-exec rm -rf {} +
+	rm -rf Bin CPackConfig.cmake CPackSourceConfig.cmake