[cmake] Pass CMAKE_CXX_STANDARD down to llvm.

Author: Axel-Naumann

interpreter/CMakeLists.txt

@@ -15,6 +15,7 @@ set(LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
 set(LLVM_INCLUDE_BENCHMARKS OFF CACHE BOOL "")
 set(CLANG_INCLUDE_TESTS OFF CACHE BOOL "")
 set(LLVM_INCLUDE_EXAMPLES OFF CACHE BOOL "")
+set(LLVM_CXX_STD "c++${CMAKE_CXX_STANDARD}" CACHE BOOL "")
 set(CLANG_BUILD_TOOLS OFF CACHE BOOL "")
 # It looks like that turning off CLANG_BUILD_TOOLS is not enough.
 set(CLANG_TOOL_ARCMT_TEST_BUILD OFF CACHE BOOL "")