--- a/make/autoconf/flags-cflags.m4	Thu Oct 17 20:27:44 2019 +0100
+++ b/make/autoconf/flags-cflags.m4	Thu Oct 17 20:53:35 2019 +0100
@@ -121,11 +121,7 @@
     # -g0 enables debug symbols without disabling inlining.
     CFLAGS_DEBUG_SYMBOLS="-g0 -xs"
   elif test "x$TOOLCHAIN_TYPE" = xxlc; then
-    if test "x$XLC_USES_CLANG" = xtrue; then
-      CFLAGS_DEBUG_SYMBOLS="-g1"
-    else
-      CFLAGS_DEBUG_SYMBOLS="-g"
-    fi
+    CFLAGS_DEBUG_SYMBOLS="-g1"
   elif test "x$TOOLCHAIN_TYPE" = xmicrosoft; then
     CFLAGS_DEBUG_SYMBOLS="-Z7 -d2Zi+"
   fi
@@ -229,7 +225,7 @@
       ;;
 
     xlc)
-      DISABLE_WARNING_PREFIX="-qsuppress="
+      DISABLE_WARNING_PREFIX="-Wno-"
       CFLAGS_WARNINGS_ARE_ERRORS="-qhalt=w"
 
       # Possibly a better subset than "all" is "lan:trx:ret:zea:cmp:ret"
@@ -576,10 +572,10 @@
 
   elif test "x$TOOLCHAIN_TYPE" = xxlc; then
     # Suggested additions: -qsrcmsg to get improved error reporting
-    TOOLCHAIN_CFLAGS_JDK="-qchars=signed -qfullpath -qsaveopt -qstackprotect"  # add on both CFLAGS
-    TOOLCHAIN_CFLAGS_JVM="-qtune=balanced \
-        -qalias=noansi -qstrict -qtls=default -qlanglvl=c99vla \
-        -qlanglvl=noredefmac -qnortti -qnoeh -qignerrno -qstackprotect"
+    # set -qtbtable=full for a better traceback table/better stacks in hs_err when xlc16 is used
+    TOOLCHAIN_CFLAGS_JDK="-qtbtable=full -qchars=signed -qfullpath -qsaveopt -qstackprotect"  # add on both CFLAGS
+    TOOLCHAIN_CFLAGS_JVM="-qtbtable=full -qtune=balanced \
+        -qalias=noansi -qstrict -qtls=default -qnortti -qnoeh -qignerrno -qstackprotect"
   elif test "x$TOOLCHAIN_TYPE" = xmicrosoft; then
     TOOLCHAIN_CFLAGS_JVM="-nologo -MD -MP"
     TOOLCHAIN_CFLAGS_JDK="-nologo -MD -Zc:wchar_t-"