AArch64: fastdebug build fails after JDK-8247645

1. linux-aarch64 gcc version
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/aarch64-linux-gnu/9/lto-wrapper
Target: aarch64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 9.4.0-1ubuntu1~20.04.1' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,gm2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-9 --program-prefix=aarch64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libquadmath --disable-libquadmath-support --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --enable-fix-cortex-a53-843419 --disable-werror --enable-checking=release --build=aarch64-linux-gnu --host=aarch64-linux-gnu --target=aarch64-linux-gnu
Thread model: posix
gcc version 9.4.0 (Ubuntu 9.4.0-1ubuntu1~20.04.1)

2. OpenJDK configure options:
$ sh configure --with-debug-level=fastdebug --with-jvm-variants=server --with-target-bits=64 --enable-unlimited-crypto --with-native-debug-symbols=internal --disable-precompiled-headers --with-boot-jdk=/home/realfyang/tools/boot-jdk --with-jtreg=/home/realfyang/tools/jtreg/build/images/jtreg --with-gtest=/home/realfyang/tools/googletest

3. OpenJDK build warnings/errors:

In file included from /home/realfyang/openjdk-jdk/src/hotspot/share/asm/assembler.hpp:475,
                 from /home/realfyang/openjdk-jdk/src/hotspot/share/asm/macroAssembler.hpp:28,
                 from /home/realfyang/openjdk-jdk/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp:27:
/home/realfyang/openjdk-jdk/src/hotspot/cpu/aarch64/assembler_aarch64.hpp: In member function 'u_char* StubGenerator::generate_chacha20Block_blockpar()':
/home/realfyang/openjdk-jdk/src/hotspot/cpu/aarch64/assembler_aarch64.hpp:2420:9: error: 'Rm' is used uninitialized in this function [-Werror=uninitialized]
 2420 | int Rm;
      | ^~
cc1plus: all warnings being treated as errors
make[3]: *** [lib/CompileJvm.gmk:147: /home/realfyang/openjdk-jdk/build/linux-aarch64-server-fastdebug/hotspot/variant-server/libjvm/objs/stubGenerator_aarch64.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [make/Main.gmk:252: hotspot-server-libs] Error 2

ERROR: Build failed for target 'images' in configuration 'linux-aarch64-server-fastdebug' (exit code 2)

=== Output from failing command(s) repeated here ===
* For target hotspot_variant-server_libjvm_objs_stubGenerator_aarch64.o:
In file included from /home/realfyang/openjdk-jdk/src/hotspot/share/asm/assembler.hpp:475,
                 from /home/realfyang/openjdk-jdk/src/hotspot/share/asm/macroAssembler.hpp:28,
                 from /home/realfyang/openjdk-jdk/src/hotspot/cpu/aarch64/stubGenerator_aarch64.cpp:27:
/home/realfyang/openjdk-jdk/src/hotspot/cpu/aarch64/assembler_aarch64.hpp: In member function 'u_char* StubGenerator::generate_chacha20Block_blockpar()':
/home/realfyang/openjdk-jdk/src/hotspot/cpu/aarch64/assembler_aarch64.hpp:2420:9: error: 'Rm' is used uninitialized in this function [-Werror=uninitialized]
 2420 | int Rm;
      | ^~
cc1plus: all warnings being treated as errors

* All command lines available in /home/realfyang/openjdk-jdk/build/linux-aarch64-server-fastdebug/make-support/failure-logs.
=== End of repeated output ===

No indication of failed target found.
HELP: Try searching the build log for '] Error'.
HELP: Run 'make doctor' to diagnose build problems.

make[1]: *** [/home/realfyang/openjdk-jdk/make/Init.gmk:320: main] Error 2
make: *** [/home/realfyang/openjdk-jdk/make/Init.gmk:186: images] Error 2