build: fix msvc build

Fix configure to set DST_PATH to the Windows style path when building with MSVC

Fixes ticket #5180.
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

configure

@@ -6233,6 +6233,12 @@ enabled stripping || strip="echo skipping strip"
 
 config_files="$TMPH config.mak doc/config.texi"
 
+if enabled msvc; then
+    dst_path=$(pwd -W)
+else
+    dst_path=$(pwd)
+fi
+
 cat > config.mak <<EOF
 # Automatically generated by configure - do not modify!
 ifndef FFMPEG_CONFIG_MAK
@@ -6251,7 +6257,7 @@ SRC_PATH=$source_path
 ifndef MAIN_MAKEFILE
 SRC_PATH:=\$(SRC_PATH:.%=..%)
 endif
-DST_PATH=$(pwd)
+DST_PATH=$dst_path
 CC_IDENT=$cc_ident
 ARCH=$arch
 INTRINSICS=$intrinsics