RFR: JDK-8073021: add native code coverage target into makefiles

[Erik Joelsson]

Hello,

Please review this patch. A new configure parameter 
--enable-native-coverage is introduced. Setting it only works when using 
gcc, for now. It adds '-fprofile-arcs -ftest-coverage -fno-inline' to 
compiler flags and '-fprofile-arcs' to linker flags, for both jdk and 
hotspot native libraries (but not for native test libraries). Setting 
this causes gcc to generate code coverage instrumentation into the 
binaries as well as generating a .gcno file for each object file 
created. The gcno files are needed for converting gathered coverage data 
into a comprehensible report. When native coverage is active, a new 
image containing the .gcno files is created by the images target.

Bug: https://bugs.openjdk.java.net/browse/JDK-8073021
Webrev: http://cr.openjdk.java.net/~erikj/8073021/webrev.root.01/

/Erik