Use -Bsymbolic-functions and -Bsymbolic

This avoids dynamic lookups to resolve symbols inside the library, but
disallows symbol interposition.

* m4/symbolic.m4: New file.
* buddy/m4/symbolic.m4: New link.
* configure.ac, buddy/configure.ac: Add AX_SYMBOLIC.
* buddy/src/Makefile.am, iface/ltsmin/Makefile.am, src/Makefile.am,
wrap/python/Makefile.am: Link with $(SYMBOLIC_LDFLAGS).

buddy/configure.ac

@@ -19,6 +19,7 @@ AC_PROG_YACC
 AC_PROG_CXX
 
 LT_INIT([win32-dll])
+AX_BSYMBOLIC
 
 # Use -Werror since using -fvisibility under MinGW is only a warning.
 # (The option is ignored anyway since this does not make sense under windows).

buddy/m4/symbolic.m4

@@ -0,0 +1 @@
+../../m4/symbolic.m4

buddy/src/Makefile.am

@@ -5,7 +5,7 @@ BUDDY_FLAGS = -I$(top_builddir) -DVERSION=23 -DBUDDY_DLL_EXPORTS -DBUDDY_DLL
 lib_LTLIBRARIES = libbddx.la
 # See the `Updating version info' node of the Libtool manual before
 # changing this.
-libbddx_la_LDFLAGS = -no-undefined -version-info 0:0:0
+libbddx_la_LDFLAGS = -no-undefined -version-info 0:0:0 $(SYMBOLIC_LDFLAGS)
 libbddx_la_CPPFLAGS = $(BUDDY_FLAGS)
 libbddx_la_SOURCES = \
  bddio.c \