Running a micro with multiple flags in JAVA_- or VM_OPTIONS results in a parsing error:

make test TEST=micro:FloatingDecimal.randomDoubleToString MICRO="VM_OPTIONS=-Xmx4g -Xms4g"
Building configuration 'linux-x64' (matching CONF_NAME=linux-x64)
Building configuration 'linux-x64' (matching CONF_NAME=linux-x64)
Building target 'test' in configuration 'linux-x64'
Running tests using MICRO control variable 'VM_OPTIONS=-Xmx4g -Xms4g'
Test selection 'micro:FloatingDecimal.randomDoubleToString', will run:
* micro:FloatingDecimal.randomDoubleToString

Running test 'micro:FloatingDecimal.randomDoubleToString'
Error parsing command line:
 'X' is not a recognized option

Quoting the values using $(call ShellQuote, $$... $$..) seem like the right thing to do here.