RFR: JDK-8238542 When warning about C/C++ compiler mismatch, be clear if this is about build compilers

Wed Feb 5 11:08:16 UTC 2020

I ran into the check that verifies that the C and C++ compilers are from 
the same version, but the output was duplicated. It turns out we check 
both the normal toolchain and the build toolchain (of course), but we 
are not clear in the output what we are complaining about.

Bug: https://bugs.openjdk.java.net/browse/JDK-8238542
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8238542-version-check-should-mention-build-compilers/webrev.01

/Magnus