8004147: test/Makefile jtreg_tests target does not work with cygwin

Reviewed-by: ctornqvi, brutisso

test/Makefile

@@ -189,9 +189,9 @@ jtreg_tests: prep $(JT_HOME) $(PRODUCT_HOME) $(JTREG)
 	$(JTREG) -a -v:fail,error               \
           $(JTREG_KEY_OPTION)                   \
           $(EXTRA_JTREG_OPTIONS)                \
-          -r:$(ABS_TEST_OUTPUT_DIR)/JTreport    \
-          -w:$(ABS_TEST_OUTPUT_DIR)/JTwork      \
-          -jdk:$(PRODUCT_HOME)                  \
+          -r:$(shell $(GETMIXEDPATH) "$(ABS_TEST_OUTPUT_DIR)")/JTreport    \
+          -w:$(shell $(GETMIXEDPATH) "$(ABS_TEST_OUTPUT_DIR)")/JTwork      \
+          -jdk:$(shell $(GETMIXEDPATH) "$(PRODUCT_HOME)")                  \
           $(JAVA_OPTIONS:%=-vmoption:%)         \
           $(JTREG_TESTDIRS)                     \
 	  || $(BUNDLE_UP_FAILED)