Fix check on AIX to determine if a file system is local

[sxa]

Assuming modifying generated-configure.sh is valid, this will fix the fact that AIX currently claims it's output directory is not on a local filesystem when it really is.

Alternative solution 1: Use /usr/sysv/bin/df (which doesn't work unless you specify the root of the mounted file system)
Alternative solution 2: Implement a check for the validity of df -l and do the check on the basis of that instead of the OPENJDK_BUILD_OS_ENV variable.

Fixes adoptium/temurin-build#181 in this repo. When accepted I'll replicate in https://github.com/adoptopenjdk/openjdk-jdk8u and https://github.com/ibmruntimes/openj9-openjdk-jdk9

[gdams]

Is it worth trying to fix upstream first? It seems to be a fix that any AIX user will use

[sxa]

Yep that would be the best approach - https://bugs.openjdk.java.net/browse/JDK-8189619 raised to cover that