aix,test: skip test due to file size limit

The test requires a file size limit that is greater than the string
size limit. Some aix machines might not meet this criteria so in
which case we should skip the test.

test/sequential/test-fs-readfile-tostring-fail.js

@@ -8,7 +8,10 @@ if (!common.enoughTestMem)
 const assert = require('assert');
 const fs = require('fs');
 const path = require('path');
+const cp = require('child_process');
 const kStringMaxLength = process.binding('buffer').kStringMaxLength;
+if (common.isAIX && Number(cp.execSync('ulimit -f')) < kStringMaxLength)
+  common.skip('intensive toString tests due to file size confinements');
 
 common.refreshTmpDir();