build: allow shared libbitcoinkernel but not by default

This keeps libtool from building all objects twice by default.

To get shared libs, configure with --enable-shared. In that case two copies may
be built.

Note: this affects the libbitcoinconsensus build as well, users who require
shared libs should add --enable-shared.

configure.ac

@@ -104,7 +104,7 @@ AC_PROG_OBJCXX
 dnl OpenBSD ships with 2.4.2
 LT_PREREQ([2.4.2])
 dnl Libtool init checks.
-LT_INIT([pic-only win32-dll])
+LT_INIT([pic-only win32-dll disable-shared])
 
 dnl Check/return PATH for base programs.
 AC_PATH_TOOL([AR], [ar])

src/Makefile.am

@@ -811,7 +811,7 @@ lib_LTLIBRARIES += $(LIBBITCOINKERNEL)
 # TODO: For now, only build a static version of this library with -all-static.
 #       There are unresolved problems when building dll's on mingw-w64 and
 #       attempting to statically embed libstdc++, libpthread, etc.
-libbitcoinkernel_la_LDFLAGS = $(AM_LDFLAGS) -all-static $(RELDFLAGS) $(PTHREAD_FLAGS)
+libbitcoinkernel_la_LDFLAGS = $(AM_LDFLAGS) $(RELDFLAGS) $(PTHREAD_FLAGS) -no-undefined
 
 libbitcoinkernel_la_LIBADD = $(LIBBITCOIN_CRYPTO) $(LIBUNIVALUE) $(LIBLEVELDB) $(LIBMEMENV) $(LIBSECP256K1)
 libbitcoinkernel_la_CPPFLAGS = $(AM_CPPFLAGS) -I$(builddir)/obj -I$(srcdir)/secp256k1/include -DBUILD_BITCOIN_INTERNAL $(BOOST_CPPFLAGS) $(LEVELDB_CPPFLAGS) -I$(srcdir)/$(UNIVALUE_INCLUDE_DIR_INT)