RFR: JDK-8217613: [AOT] TEST_OPTS_AOT_MODULES doesn't work on mac

[Erik Joelsson]

The TEST_OPTS=AOT_MODULES option does not work when running tests 
locally on Macosx. This is because jaot expects the linker to be "ld", 
while we define the linker (LD) to be clang on Macosx. When running 
tests on already built JDKs using run-test-prebuilt, we already setup LD 
to point to "ld" rather than "clang", so the same should be done when 
running local tests.

This patch rewrites LD for jaotc, on Macosx and Linux. Though we did not 
have a problem on Linux, the run-test-prebuilt case does set LD to "ld" 
on Linux so better have it consistent.

I also added -XX:+UnlockDiagnosticVMOptions to the verification command 
to make it work on release builds where this flag is default off, as 
well as cleaned up some whitespace.

Bug: https://bugs.openjdk.java.net/browse/JDK-8217613

Webrev: http://cr.openjdk.java.net/~erikj/8217613/webrev.01/

/Erik