common: Fix build problem with Sun Studio compiler.

* common/estream.c (ESTREAM_MUTEX_UNLOCK): Use int dummy dummy
functions.
(ESTREAM_MUTEX_INITIALIZE): Ditto.

(cherry picked from commit 571bcd4662a351cfa55bbf1a79ed1bc26da5780f)

Reolved conflicts:
common/estream.c

Warning: estream.c still uses pth_mutex_* which is definitely wrong.

Needs to be investigated.

• GnuPG-bug-id: T1566
• Signed-off-by: Werner Koch <wk@gnupg.org>