Add *.d.tmp files to .gitignore

These are temporary files generated by the build process that should not
be checked in.
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11122)

(cherry picked from commit 7b5108dff4cfde059ca278147a188fb6254603d1)

.gitignore

@@ -178,6 +178,7 @@ Makefile.save
 *.bak
 cscope.*
 *.d
+*.d.tmp
 pod2htmd.tmp
 
 # Windows manifest files