don't suppress shared libc when linker lacks -Bsymbolic-functions

previous work overhauling the dynamic linker made it so that linking
libc with -Bsymbolic-functions was no longer mandatory, but the
configure logic that forced --disable-shared when ld failed to accept
the option was left in place.

this commit removes the hard-coded -Bsymbolic-functions from the
Makefile and changes the configure test to one that simply adds it to
the auto-detected LDFLAGS on success.

configure

@@ -565,15 +565,10 @@ tryldflag LDFLAGS_AUTO -Wl,--no-undefined
 # versions built without shared library support and pcc are broken.
 tryldflag LDFLAGS_AUTO -Wl,--exclude-libs=ALL
 
-test "$shared" = "no" || {
-# Disable dynamic linking if ld is broken and can't do -Bsymbolic-functions
-LDFLAGS_DUMMY=
-tryldflag LDFLAGS_DUMMY -Wl,-Bsymbolic-functions || {
-test "$shared" = "yes" && fail "$0: error: linker cannot build shared library"
-printf "warning: disabling dynamic linking support\n"
-shared=no
-}
-}
+# Linking with -Bsymbolic-functions is no longer mandatory for
+# the dynamic linker to work, but enable it if it works as
+# a linking optimization.
+tryldflag LDFLAGS_AUTO -Wl,-Bsymbolic-functions
 
 # Find compiler runtime library
 test -z "$LIBCC" && tryldflag LIBCC -lgcc && tryldflag LIBCC -lgcc_eh