[foreign-memaccess] RFR 8219852: Create a set of standard benchmarks

[Jorn Vernee]

Hi,

Please review the following patch that adds several benchmarks for 
measuring things like; offheap access, allocation, and deallocation of 
the memory access API vs. other implementations like ByteBuffer and JNI.

Bug: https://bugs.openjdk.java.net/browse/JDK-8219852
Webrev:

This also includes a small build system fix to support using native 
libraries in the benchmarks (which can be upstreamed as well).

Benchmarks can be ran after configuring with 
`--with-jmh=/path/to/jmh/jars`. The needed jars are commons-math3 [1], 
jmh-core [2], jmh-generator-annprocess [3], and jopt-simple [4]. After 
configuring, benchmarks can be ran with `make test 
TEST="micro:java.foreign" MICRO="VM_OPTIONS=--add-modules 
jdk.incubator.foreign"`.

Thanks,
Jorn

[1] : https://mvnrepository.com/artifact/org.apache.commons/commons-math3
[2] : https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-core
[3] : 
https://mvnrepository.com/artifact/org.openjdk.jmh/jmh-generator-annprocess
[4] : https://mvnrepository.com/artifact/net.sf.jopt-simple/jopt-simple