RFR(M/L) : 8209611 : use C++ compiler for hotspot tests

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8209611/webrev.01/index.html
> 11160 lines changed: 879 ins; 61 del; 10220 mod;

Hi all,

could you please review the patch which moves all hotspot native test code to C++? this will guarantee that we always use C++ compilers for them (as an opposite to either C or C++ compiler depending on configuration), as a result we will be able to get rid of JNI_ENV_ARG[1] macros, perform other clean ups and improve overall quality of the test code.

the patch consists of two parts:
 - automatic: renaming .c files to .cpp, updating #include, changing JNI/JVMTI calls
 - semi-manual: adding extern "C" , fixing a number of compiler warnings (mostly types inconsistency), updating makefiles

JBS: https://bugs.openjdk.java.net/browse/JDK-8209611
webrevs:
 - automatic: http://cr.openjdk.java.net/~iignatyev//8209611/webrev.00/index.html
> 9394 lines changed: 0 ins; 0 del; 9394 mod; 

 - semi-manual: http://cr.openjdk.java.net/~iignatyev//8209611/webrev.0-1/index.html
> 1899 lines changed: 879 ins; 61 del; 959 mod

 - whole: http://cr.openjdk.java.net/~iignatyev//8209611/webrev.01/index.html
> 11160 lines changed: 879 ins; 61 del; 10220 mod;

testing: all hotspot tests + tier[1-3]

[1] https://bugs.openjdk.java.net/browse/JDK-8209547

Thanks,
-- Igor