Make 'make clean' wipe all object files in src/*/

Instead of naming the subdirectories explicitly (which will result in
us forgetting about one sooner or later), we change the shell glob
pattern to wipe all object files from all subdirectories under src/.

Signed-off-by: Andreas Ericsson <ae@op5.se>

Makefile

@@ -94,7 +94,7 @@ clean:
 	rm -f $(GIT_LIB)
 	rm -f libgit2.pc
 	rm -f *.pdb
-	rm -f src/*.o src/sha1/*.o src/unix/*.o src/win32/*.o
+	rm -f src/*.o src/*/*.o
 	rm -rf apidocs
 	rm -f *~ src/*~ src/git/*~ src/sha1/*~ src/unix/*~ src/win32/*~
 	@$(MAKE) -C tests -s --no-print-directory clean