Linux GCC/Clang no member named 'make_unique' in namespace 'std'

[danilw]

Fix:
add to RadeonRays/CMakeLists.txt and Baikal/CMakeLists.txt

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

and OpenEXR not listed in build dependencies

also RadeonProRender-Baikal broken in GCC-8 GCC-9 and Clang9, Ihave build it only in gcc-7

and to RprTest/basic.h va_start was not declared in this scope
add #include <cstdarg>