RFR: 9+8u: Fix build error in MacroAssembler::needs_explicit_null_check

[Aleksey Shipilev]

i586 build fails with:

jdk8u/hotspot/src/share/vm/asm/assembler.cpp:323: error: integer constant is too
large for ‘unsigned long’ type
jdk8u/hotspot/src/share/vm/asm/assembler.cpp: In static member function ‘static
bool MacroAssembler::needs_explicit_null_check(intptr_t)’:
jdk8u/hotspot/src/share/vm/asm/assembler.cpp:323: error: large integer
implicitly truncated to unsigned type

Fix:
  http://cr.openjdk.java.net/~shade/shenandoah/build/masm-null-check/webrev.01/

This affects both 9 and 8u.

Testing: hotspot_gc_shenandoah/fastdebug with 9 and 8u

Thanks,
-Aleksey