RFR(S) : 8219391 : extend gcov support to llvm/clang

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8219391/webrev.00
> 21 lines changed: 3 ins; 0 del; 18 mod;

Hi all,

could you please review this small and trivial patch which allows usage of --enable-native-coverage configure option w/ clang devkit?

> llvm/clang supports gcov in the same way gcc does, it has the same compiler/linker options to enable code coverage information, produces the same .gcda files; the produced binaries generate .gcdo files and treat env. variables in the same way.

webrev: http://cr.openjdk.java.net/~iignatyev//8219391/webrev.00
JBS: https://bugs.openjdk.java.net/browse/JDK-8219391
testing: built on mac w/ --enable-native-coverage, run some tests and spot-checked coverage

Thanks,
-- Igor