Merge #15683: Comment for seemingly duplicate LIBBITCOIN_SERVER

2a1408c Comment for seemingly duplicate LIBBITCOIN_SERVER (Peter Bushnell)

Pull request description:

  Added a comment to explain the addition of LIBBITCOIN_SERVER twice in bitcoind_LDADD which seems incorrect at a glance until the behaviour of Linux linkers is understood.

ACKs for commit 2a1408:
  practicalswift:
    ACK 2a1408c
  MarcoFalke:
    ACK 2a1408c
  fanquake:
    utACK 2a1408c
  ryanofsky:
    utACK 2a1408c

Tree-SHA512: dd2a7f61d53ce8882a56c831c32e1f48e9eab741ef21361f195c38bb455abdc4bc524d3b44b6f69c7498898cd871a23c39d215de28db3b20ef5fd2135d5e136a

Author: MarcoFalke

src/Makefile.am

@@ -497,6 +497,8 @@ if TARGET_WINDOWS
 bitcoind_SOURCES += bitcoind-res.rc
 endif
 
+# Libraries below may be listed more than once to resolve circular dependencies (see
+# https://eli.thegreenplace.net/2013/07/09/library-order-in-static-linking#circular-dependency)
 bitcoind_LDADD = \
   $(LIBBITCOIN_SERVER) \
   $(LIBBITCOIN_WALLET) \