[11u] RFR: 8266713: [AIX] Build failure after 11u backport of JDK-8247753

[Severin Gehwolf]

Hi,

Please review this AIX build fix for OpenJDK 11u. The JDK 11u backport
of JDK-8247753 included a call to strcasestr for case-insensitive
comparison of the set XDG_CURRENT_DESKTOP environment variable.
Unfortunately, strcasestr is a GNU extension and isn't available on
AIX. The proposed fix is to implement a version of strcasestr AIX-local
in java_props_md.c. Note that this is a JDK 11u-specific bug since the
backport of JDK-8247753 is different to the version in later JDKs where
this comparison is not done in native code, but in Java.

Bug: https://bugs.openjdk.java.net/browse/JDK-8266713
webrev: https://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8266713/02/webrev/

AIX failed to build prior this patch and builds with this patch after.
Manual sanity checks for the strcasestr() impl.

Thoughts?

Thanks,
Severin