Move the iconv test to the bottom of configure.

This fixes a possible mis-detection of iconv on OS X.
OS X with macports often has two version of libiconv.2.dylib
installed, one with symbols like "_iconv_open" and one with
"_libiconv_open", so test for iconv with all flags to make
sure the detection uses the same library as the actual
compilation / linking.

Tested-by: Paul Sturbaum

configure

@@ -3888,7 +3888,6 @@ enabled avisynth   && require2 vfw32 "windows.h vfw.h" AVIFileInit -lavifil32
 enabled fontconfig && require_pkg_config fontconfig "fontconfig/fontconfig.h" FcInit
 enabled frei0r     && { check_header frei0r.h || die "ERROR: frei0r.h header not found"; }
 enabled gnutls     && require_pkg_config gnutls gnutls/gnutls.h gnutls_global_init
-enabled iconv      && { check_func_headers iconv.h iconv || check_lib2 iconv.h iconv -liconv || die "ERROR: iconv not found"; }
 enabled libiec61883 && require libiec61883 libiec61883/iec61883.h iec61883_cmp_connect -lraw1394 -lavc1394 -lrom1394 -liec61883
 enabled libaacplus && require  "libaacplus >= 2.0.0" aacplus.h aacplusEncOpen -laacplus
 enabled libass     && require_pkg_config libass ass/ass.h ass_library_init
@@ -4053,6 +4052,9 @@ enabled vdpau &&
     check_cpp_condition vdpau/vdpau.h "defined VDP_DECODER_PROFILE_MPEG4_PART2_ASP" ||
     disable vdpau
 
+# Funny iconv installations are not unusual, so check it after all flags have been set
+enabled iconv && { check_func_headers iconv.h iconv || check_lib2 iconv.h iconv -liconv || die "ERROR: iconv not found"; }
+
 enabled debug && add_cflags -g"$debuglevel" && add_asflags -g"$debuglevel"
 enabled coverage && add_cflags "-fprofile-arcs -ftest-coverage" && add_ldflags "-fprofile-arcs -ftest-coverage"
 test -n "$valgrind" && target_exec="$valgrind --error-exitcode=1 --malloc-fill=0x2a --track-origins=yes --leak-check=full --gen-suppressions=all --suppressions=$source_path/tests/fate-valgrind.supp"