RFR: JDK-8205055: Fix compilation optimization errors with new Solaris toolchain

[gary.adams at oracle.com]

Locally tested the fix below and via mach5 jobs.
The ~50 failed tests all completed successfully.
It'd be good for Erik to repeat his full testing with
this patch included in case it blocked other issues
from being observed.

This fix can be integrated after the sync from jdk/client.

  Issue: https://bugs.openjdk.java.net/browse/JDK-8205055

Proposed fix:

diff --git a/make/hotspot/lib/JvmOverrideFiles.gmk 
b/make/hotspot/lib/JvmOverrideFiles.gmk
--- a/make/hotspot/lib/JvmOverrideFiles.gmk
+++ b/make/hotspot/lib/JvmOverrideFiles.gmk
@@ -74,6 +74,8 @@

  else ifeq ($(OPENJDK_TARGET_OS), solaris)
    ifneq ($(DEBUG_LEVEL), slowdebug)
+ # dev studio 12.6 workaround
+ BUILD_LIBJVM_arguments.cpp_OPTIMIZATION := LOW