do not remove links found in .git directory

Some setups use links inside .git directory and make clean should not
remove them to avoid breaking git meta-information.
Signed-off-by: NCristian Stoica <cristian.stoica@nxp.com>

CLA: none; trivial
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1078)

Configurations/unix-Makefile.tmpl

@@ -259,7 +259,7 @@ clean: libclean
 	rm -f core
 	rm -f tags TAGS
 	rm -f openssl.pc libcrypto.pc libssl.pc
-	-rm -f `find . -type l`
+	-rm -f `find . -type l -a \! -path "./.git/*"`
 	rm -f $(TARFILE)
 
 # This exists solely for those who still type 'make depend'