Oracle Studio 12.6 produces an Assertion in ../lnk/constexpr.cc when compiling ICU 64.1.
I have reduced it down to the following t.cpp:
static constexpr char16_t kFallbackPaddingString[] = u" ";
$ CC -V && CC -std=c++11 -c t.cpp
CC: Studio 12.6 Sun C++ 5.15 SunOS_i386 2017/05/30
>> Assertion: (../lnk/constexpr.cc, line 875)
while processing t.cpp at line 1.
Verified it doesn't fail with Oracle Studio 12.4 or gcc 4.8 .