Convert MJIT_CC to Windows path on msys too

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65607 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.ac

@@ -255,8 +255,8 @@ AC_SUBST(CSRCFLAG)
 : ${MJIT_CC=$CC}
 AS_IF([test "x$cross_compiling" = xno], [
     AC_PATH_PROG([MJIT_CC], ${MJIT_CC-$CC})
-    AS_CASE([$build_os:$host_os],
-	[*cygwin*:*mingw*], [MJIT_CC=`cygpath -ma $MJIT_CC`])
+    AS_CASE([$target_os],
+	[*mingw*], [command -v cygpath && MJIT_CC=`cygpath -ma $MJIT_CC`])
     shift 2
     MJIT_CC="$MJIT_CC${1+ }$*"
 ])