configure: Silence warnings about constant unsigned overflows in MSVC

unsigned overflows are well defined in C and used for example in crypto
and various other places.
None of the affected warnings currently shown points to an actual defect

untested
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -3260,6 +3260,7 @@ msvc_flags(){
             -Wall)                echo -W4 -wd4244 -wd4127 -wd4018 -wd4389     \
                                        -wd4146 -wd4057 -wd4204 -wd4706 -wd4305 \
                                        -wd4152 -wd4324 -we4013 -wd4100 -wd4214 \
+                                       -wd4307 \
                                        -wd4273 -wd4554 -wd4701 ;;
         esac
     done