[aarch64-port-dev ] RFR: Fix AArch64 build failure after JDK-8062808 backport

[Aleksey Shipilev]

My CI catches build failure in current aarch64-port/jdk8u-shenandoah:

/home/shade/aarch64-port-jdk8u-shenandoah/hotspot/src/cpu/aarch64/vm/c1_LIRAssembler_aarch64.cpp: In 
member function ‘Address LIR_Assembler::as_Address(LIR_Address*, Register)’:
/home/shade/aarch64-port-jdk8u-shenandoah/hotspot/src/share/vm/utilities/globalDefinitions_gcc.hpp:223:32: 
error: control reaches end of non-void function [-Werror=return-type]

I believe this only affects 8u aarch64 after -Wreturn-type was enabled (JDK-8062808).

Note that push to JDK 9 has the "return Address()" in the place we want, but that addition is 
missing in aarch64-port/jdk8u-shenandoah!
   https://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/d498aba2c736#l10.210

So, a trivial fix is to put in the missing addition:

diff -r 76dace090781 src/cpu/aarch64/vm/c1_LIRAssembler_aarch64.cpp
--- a/src/cpu/aarch64/vm/c1_LIRAssembler_aarch64.cpp    Tue Dec 15 20:18:10 2020 +0100
+++ b/src/cpu/aarch64/vm/c1_LIRAssembler_aarch64.cpp    Mon Jan 04 04:24:42 2021 -0500
@@ -207,6 +207,7 @@
        return Address(base, tmp, Address::lsl(addr->scale()));
      }
    }
+  return Address();
  }

I would like to push it to current aarch64-port/jdk8u-shenandoah, which is stabilizing for 8u282. I 
believe the patch is innocuous. Andrew, this might complicate the merges somewhat, please advise 
whether and when you want this patch in.

Testing: 8u aarch64 native build

-- 
Thanks,
-Aleksey