JRE-483 JBSDK does not compile with Xcode 9

Fixed Xcode 8 build failure with newer (unsupported) options
diff --git a/make/bsd/makefiles/gcc.make b/make/bsd/makefiles/gcc.make
index 3d201d2..95761ce 100644
--- a/make/bsd/makefiles/gcc.make
+++ b/make/bsd/makefiles/gcc.make
@@ -87,6 +87,7 @@
   ifeq ($(DSYMUTIL),)
     DSYMUTIL=dsymutil
   endif
+  XCODE_VER := $(shell xcodebuild -version | head -n1 | sed 's/Xcode //' | cut -d'.' -f1)
 endif
 
 ifeq ($(USE_CLANG), true)
@@ -257,7 +258,7 @@
 # Not yet supported by clang in Xcode 4.6.2
 #  WARNINGS_ARE_ERRORS += -Wno-tautological-constant-out-of-range-compare
   WARNINGS_ARE_ERRORS += -Wno-delete-non-virtual-dtor -Wno-deprecated -Wno-format -Wno-dynamic-class-memaccess
-  WARNINGS_ARE_ERRORS += -Wno-empty-body -Wno-shorten-64-to-32 -Wno-sign-conversion
+  WARNINGS_ARE_ERRORS += -Wno-empty-body
 endif
 
 WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef
@@ -267,7 +268,15 @@
   # conversions which might affect the values. Only enable it in earlier versions.
   WARNING_FLAGS = -Wunused-function
   ifeq ($(USE_CLANG),)
-    WARNING_FLAGS += -Wno-conversion -Wno-logical-op-parentheses -Wno-tautological-undefined-compare -Wno-shift-negative-value -Wno-switch -Wno-format
+     ifeq ($(OS_VENDOR), Darwin)
+       ifeq "$(shell expr $(XCODE_VER) \>= 9 )" "1"
+         WARNING_FLAGS += -Wno-conversion -Wno-logical-op-parentheses -Wno-tautological-undefined-compare -Wno-shift-negative-value -Wno-switch -Wno-format -Wno-shorten-64-to-32 -Wno-sign-conversion
+       else
+         WARNING_FLAGS += -Wconversion
+       endif
+     else
+       WARNING_FLAGS += -Wconversion
+     endif
   endif
 endif