configure: Silence Xcode warnings about duplicate libraries

Since Xcode 15, macOS developer tools use a new linker. The new
linker by default warns for duplicate -l options. As this is a
known and expected thing, not to be considered an issue, ask for
the warning to be silenced.

This silences linker warnings like this:

    ld: warning: ignoring duplicate libraries: '-lc++', '-lcrypto', '-lm', '-logg', '-lpthread', '-lssl', '-lvorbis', '-lvpx', '-lz'

The linker can also warn about duplicate -rpath options, and there's
currently no option to silence those warnings.

Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -6490,6 +6490,7 @@ check_cc intrinsics_sse2 emmintrin.h "__m128i test = _mm_setzero_si128()"
 
 check_ldflags -Wl,--as-needed
 check_ldflags -Wl,-z,noexecstack
+check_ldflags -Wl,-no_warn_duplicate_libraries
 
 if ! disabled network; then
     check_func getaddrinfo $network_extralibs