configure: add a -lstdc++ flag to the some external library checks

Two of them are missing it in their pkg-config file, so adding it
here is a workaround until said pkg-config files are fixed.

Debugged with the help of Reino Wijnsma.

Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -6030,7 +6030,7 @@ enabled libopenjpeg       && { { check_lib libopenjpeg openjpeg-2.3/openjpeg.h o
                                { check_lib libopenjpeg openjpeg-1.5/openjpeg.h opj_version -lopenjpeg -DOPJ_STATIC && add_cppflags -DOPJ_STATIC; } ||
                                { check_lib libopenjpeg openjpeg.h opj_version -lopenjpeg -DOPJ_STATIC && add_cppflags -DOPJ_STATIC; } ||
                                die "ERROR: libopenjpeg not found"; }
-enabled libopenmpt        && require_pkg_config libopenmpt "libopenmpt >= 0.2.6557" libopenmpt/libopenmpt.h openmpt_module_create
+enabled libopenmpt        && require_pkg_config libopenmpt "libopenmpt >= 0.2.6557" libopenmpt/libopenmpt.h openmpt_module_create -lstdc++ && append libopenmpt_extralibs "-lstdc++"
 enabled libopus           && {
     enabled libopus_decoder && {
         require_pkg_config libopus opus opus_multistream.h opus_multistream_decoder_create
@@ -6042,11 +6042,11 @@ enabled libopus           && {
 enabled libpulse          && require_pkg_config libpulse libpulse pulse/pulseaudio.h pa_context_new
 enabled librsvg           && require_pkg_config librsvg librsvg-2.0 librsvg-2.0/librsvg/rsvg.h rsvg_handle_render_cairo
 enabled librtmp           && require_pkg_config librtmp librtmp librtmp/rtmp.h RTMP_Socket
-enabled librubberband     && require_pkg_config librubberband "rubberband >= 1.8.1" rubberband/rubberband-c.h rubberband_new
+enabled librubberband     && require_pkg_config librubberband "rubberband >= 1.8.1" rubberband/rubberband-c.h rubberband_new -lstdc++ && append librubberband_extralibs "-lstdc++"
 enabled libshine          && require_pkg_config libshine shine shine/layer3.h shine_encode_buffer
 enabled libsmbclient      && { use_pkg_config libsmbclient smbclient libsmbclient.h smbc_init ||
                                require libsmbclient libsmbclient.h smbc_init -lsmbclient; }
-enabled libsnappy         && require libsnappy snappy-c.h snappy_compress -lsnappy
+enabled libsnappy         && require libsnappy snappy-c.h snappy_compress -lsnappy -lstdc++
 enabled libsoxr           && require libsoxr soxr.h soxr_create -lsoxr
 enabled libssh            && require_pkg_config libssh libssh libssh/sftp.h sftp_init
 enabled libspeex          && require_pkg_config libspeex speex speex/speex.h speex_decoder_init -lspeex