Output .DEF file on Win32

configure.ac

@@ -15,7 +15,7 @@ AC_SUBST(ISODATE)
 
 SODIUM_LIBRARY_VERSION_MAJOR=4
 SODIUM_LIBRARY_VERSION_MINOR=0
-
+DLL_VERSION=4
 SODIUM_LIBRARY_VERSION=4:0:0
 #                      | | |
 #               +------+ | +---+
@@ -31,6 +31,7 @@ SODIUM_LIBRARY_VERSION=4:0:0
 AC_SUBST(SODIUM_LIBRARY_VERSION_MAJOR)
 AC_SUBST(SODIUM_LIBRARY_VERSION_MINOR)
 AC_SUBST(SODIUM_LIBRARY_VERSION)
+AC_SUBST(DLL_VERSION)
 
 LX_CFLAGS=${CFLAGS-NONE}
 AC_PROG_CC_C99
@@ -132,6 +133,7 @@ AX_CHECK_LINK_FLAG([-Wl,-z,noexecstack], [LDFLAGS="$LDFLAGS -Wl,-z,noexecstack"]
 
 LT_INIT
 AC_SUBST(LIBTOOL_DEPS)
+gl_LD_OUTPUT_DEF
 
 AC_ARG_VAR([AR], [path to the ar utility])
 AC_CHECK_TOOL([AR], [ar], [ar])

src/libsodium/Makefile.am

@@ -180,5 +180,12 @@ libsodium_la_CPPFLAGS = \
 	-I$(srcdir)/include/sodium \
 	-I$(builddir)/include/sodium
 
+if HAVE_LD_OUTPUT_DEF
+	libsodium_la_LDFLAGS += -Wl,--output-def,libsodium-$(DLL_VERSION).def
+	defexecdir = $(bindir)
+	defexec_DATA = libsodium-$(DLL_VERSION).def
+	DISTCLEANFILES += $(defexec_DATA)
+endif
+
 SUBDIRS = \
 	include