hg: jdk/sandbox: 8228426: xlc: switch to clang-style warning disabling

[chris.hegarty at oracle.com]

Changeset: aaa83519e723
Author:    mbaesken
Date:      2019-07-19 11:09 +0200
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/aaa83519e723

8228426: xlc: switch to clang-style warning disabling
Reviewed-by: clanger, mdoerr

! make/autoconf/flags-cflags.m4
! make/hotspot/lib/CompileJvm.gmk
! make/lib/Awt2dLibraries.gmk