RFR(XS): 8252051: Make mlvmJvmtiUtils strncpy uses GCC 10.x friendly

[Mikael Vidstedt]

Please review this small change which updates the strncpy code in mlvmJvmtiUtils.cpp to make gcc 10.x happy:

JBS: https://bugs.openjdk.java.net/browse/JDK-8252051
webrev: http://cr.openjdk.java.net/~mikael/webrevs/8252051/webrev.00/open/webrev/

* Background (from JBS)

gcc 10.2 is producing a warning for mlvmJmvtiUtils.cpp: 

In file included from test/hotspot/jtreg/vmTestbase/vm/mlvm/indy/func/jvmti/share/libIndyRedefineClass.cpp:31: 
test/hotspot/jtreg/vmTestbase/vm/mlvm/share/mlvmJvmtiUtils.cpp:100:12: error: 'char* strncpy(char*, const char*, size_t)' specified bound 256 equals destination size [-Werror=stringop-truncation] 
  100 | strncpy(mn->classSig, szSignature, sizeof(mn->classSig)); 
      | ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
cc1plus: all warnings being treated as errors 

It seems like gcc is not smart enough to realize that the strncpy on the previous line (mn->methodName) cannot modify szSignature.


* Testing

tier1 and test/hotspot/jtreg:vmTestbase_vm_mlvm locally


Cheers,
Mikael