Index: tools/llvm-config/CMakeLists.txt
===================================================================
--- tools/llvm-config/CMakeLists.txt
+++ tools/llvm-config/CMakeLists.txt
@@ -29,12 +29,20 @@
 # Fetch target specific compile options, e.g. RTTI option
 get_property(COMPILE_FLAGS TARGET llvm-config PROPERTY COMPILE_FLAGS)
 
+# The language standard potentially affects the ABI/API of LLVM, so we want
+# to make sure it is reported by llvm-config.
+# NOTE: We don't want to start extracting any random C/CXX flags that the
+# user may add that could affect the ABI.  We only want to extract flags
+# that have been added by the LLVM build system.
+string(REGEX MATCH "-std=[^ ]\+" LLVM_CXX_STD_FLAG ${CMAKE_CXX_FLAGS})
+string(REGEX MATCH "-std=[^ ]\+" LLVM_C_STD_FLAG ${CMAKE_C_FLAGS})
+
 # Use configure_file to create BuildVariables.inc.
 set(LLVM_SRC_ROOT ${LLVM_MAIN_SRC_DIR})
 set(LLVM_OBJ_ROOT ${LLVM_BINARY_DIR})
-set(LLVM_CPPFLAGS "${CMAKE_CPP_FLAGS} ${CMAKE_CPP_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
-set(LLVM_CFLAGS "${CMAKE_C_FLAGS} ${CMAKE_C_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${LLVM_DEFINITIONS}")
-set(LLVM_CXXFLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE}} ${COMPILE_FLAGS} ${LLVM_DEFINITIONS}")
+set(LLVM_CPPFLAGS "${LLVM_DEFINITIONS}")
+set(LLVM_CFLAGS "${LLVM_C_STD_FLAG} ${LLVM_DEFINITIONS}")
+set(LLVM_CXXFLAGS "${LLVM_CXX_STD_FLAG} ${COMPILE_FLAGS} ${LLVM_DEFINITIONS}")
 set(LLVM_BUILD_SYSTEM cmake)
 set(LLVM_HAS_RTTI ${LLVM_CONFIG_HAS_RTTI})
 set(LLVM_DYLIB_VERSION "${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX}")