Change format of -X arguments to require value after '='

Report a warning when an argument is passed in the old form (with the
whitespace)

 #KT-17264 Fixed

compiler/testData/cli/jvm/pluginSimple.args

@@ -1,10 +1,9 @@
 -d
 $TEMP_DIR$
--Xplugin
-dist/kotlinc/lib/android-extensions-compiler.jar
+-Xplugin=dist/kotlinc/lib/android-extensions-compiler.jar
 -P
 plugin\:org.jetbrains.kotlin.android\:package=com.myapp
 -P
 plugin\:org.jetbrains.kotlin.android\:variant=main;$TESTDATA_DIR$/androidPlugin/res
 $TESTDATA_DIR$/pluginSimple.kt
-$TESTDATA_DIR$/androidPlugin
+$TESTDATA_DIR$/androidPlugin