8233285: Demangling C++ symbols in jhsdb jstack --mixed

http://mail.openjdk.java.net/pipermail/serviceability-dev/2019-October/029720.html
http://hg.openjdk.java.net/jdk/jdk/rev/e2dfab7beccb
http://cr.openjdk.java.net/~ysuenaga/JDK-8233285/webrev.00/

=== Output from failing command(s) repeated here ===
* For target support_native_jdk.hotspot.agent_libsaproc_LinuxDebuggerLocal.o:
g++: error: unrecognized command line option '-marm'; did you mean '-mabm'?
g++: error: unrecognized command line option '-mfloat-abi=hard'
g++: error: unrecognized command line option '-mfpu=vfp'; did you mean '-mcpu='?

* All command lines available in /ws/workspace/jdk-dev/label/linux-arm/type/b11/build/linux-arm-server-release/make-support/failure-logs.
=== End of repeated output ===

Build fails because cross-toolschain for arm32 CPU is substituted by default toolchain:
+SA_TOOLCHAIN := $(TOOLCHAIN_DEFAULT)
 $(eval $(call SetupJdkLibrary, BUILD_LIBSA, \
+ TOOLCHAIN := $(SA_TOOLCHAIN), \