8299616: [11u] Bootcycle build fails after JDK-8257679 backport

Reviewed-by: andrew, clanger

Author: shipilev

make/autoconf/bootcycle-spec.gmk.in

@@ -28,11 +28,19 @@
 # First include the real base spec.gmk file
 include @SPEC@
 
-# Override specific values to do a boot cycle build
+# Check that the user did not try to specify a different java to use for compiling.
+# On windows we need to account for fixpath being first word.
+ifeq ($(firstword $(JAVA)),$(FIXPATH))
+  JAVA_EXEC_POS=2
+else
+  JAVA_EXEC_POS=1
+endif
 ifneq ($(word $(JAVA_EXEC_POS),$(SJAVAC_SERVER_JAVA)),$(word $(JAVA_EXEC_POS),$(JAVA)))
   $(error Bootcycle builds are not possible if --with-sjavac-server-java is specified)
 endif
 
+# Override specific values to do a boot cycle build
+
 # Use a different Boot JDK
 BOOT_JDK := $(JDK_IMAGE_DIR)