Contributed_Sample_Codes/Tutorial1/pi: c++ compile error

[tonycurtis]

With community PGI on Fedora 30 x86_64

$ make c++
pgc++ -o pic.exe pic.cpp -fast -Minfo=opt
"/usr/include/c++/9/bits/stl_function.h", line 437: error: identifier
          "__builtin_is_constant_evaluated" is undefined
  	if (__builtin_is_constant_evaluated())
  	    ^

1 error detected in the compilation of "pic.cpp".
make: *** [Makefile:14: pic.exe] Error 2

$ pgc++ -V

pgc++ 19.4-0 LLVM 64-bit target on x86-64 Linux -tp skylake
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