RFR(S): 8252407: Build failure with gcc-8+ and asan

[Eric Liu]

Hi all,

Please review this simple change to fix some compile warnings.

The newer gcc (gcc-8 or higher) would warn for calls to bounded string
manipulation functions such as 'strncpy' that may either truncate the
copied string or leave the destination unchanged.

This patch fixed stringop-truncation warnings reported by gcc, some of
them only appear when compiled with "--enable-asan".

[TESTS]
Jtreg: hotspot::hotspot_all_no_apps, jdk::jdk_core and langtools::tier1.
No new failure found.

http://cr.openjdk.java.net/~qfeng/ericliu/jdk/stringop_trunc/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8252407

Thanks,
Eric