RFR(S) : 8245610 : remove in-tree copy on gtest

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev/8245610/webrev.00/
> 132 lines changed: 80 ins; 36 del; 16 mod
http://cr.openjdk.java.net/~iignatyev/8245610/webrev.00%2bremoval/
> 57482 lines changed: 80 ins; 57385 del; 17 mod;

Hi all,

could you please review this small (if you ignore removal part) patch which removes in-tree copy of gtest (test/fmw/gtest) and updates makefiles to use one provided thru an added configure option `--with-gtest`? the previously used configure option `--enable-hotspot-gtest` gets depricated.

the patch also compiles gtest and gmock source code into a static library so they can be compiled w/ all warnings disabled.

from JBS:
> w/ JEP 381 (JDK-8241787 / JDK-8244224) being integrated, all compilers used by OpenJDK became supported by gtest out-of-box, so there is no need to have our copy of gtest framework (including gmock) within OpenJDK source tree. instead, it can be treated like any other external dependencies, and a pointer to the directory w/ gtest code can be passed via configure options. 


JBS: https://bugs.openjdk.java.net/browse/JDK-8245610
webrevs:
 - http://cr.openjdk.java.net/~iignatyev/8245610/webrev.00/ (meaningful changes)
 - http://cr.openjdk.java.net/~iignatyev/8245610/webrev.00%2bremoval/ (all changes)
testing: 
- gtest tests on {linux,windows,macosx}-x64; 
- tier[1-5] builds which include but not limited to linux-aarch64, linux-arm32, linux-x64-zero

Thanks,
-- Igor