fixed error reporting in src instead of _build

Makefile.win

@@ -27,7 +27,7 @@ FILTER=sed 's/File "\([^"]\+\)", line \([0-9]\+\), \(.*\)/\1(\2): \3/' tmp.cmi
 endif
 
 ifeq (${FD_OUTPUT}, 1)
-FILTER=sed '/File/{ N; s/File "\([^"]\+\)", line \([0-9]\+\), characters \([0-9-]\+\):[\r\n]*\(.*\)/\1:\2: characters \3 : \4/ }' tmp.cmi
+FILTER=sed -e '/File/{ N; s/File "\([^"]\+\)", line \([0-9]\+\), characters \([0-9-]\+\):[\r\n]*\(.*\)/\1:\2: characters \3 : \4/ }' -e 's/_build\/src\//src\//' tmp.cmi
 endif
 
 ifdef FILTER