configure: Set the right cc_e flags for msvc

The default ones work, but outputs the preprocessed file on stdout
(into config.log).

Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -2317,6 +2317,7 @@ probe_cc(){
             _ld_o='-Fe$@'
         fi
         _cc_o='-Fo $@'
+        _cc_e='-P -Fi $@'
         _flags_filter=msvc_flags
         _ld_lib='lib%.a'
         _ld_path='-libpath:'