diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -59,6 +59,8 @@
   if(LLVM_ENABLE_ZLIB)
     find_package(ZLIB REQUIRED)
   endif()
+  option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
+  option(LLVM_ENABLE_WERROR "Fail and stop if a warning is triggered." ON)
 
   include(CMakeParseArguments)
   include(AddLLVM)
@@ -76,7 +78,6 @@
       NO_DEFAULT_PATH)
   endif()
 
-  option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
   option(LLVM_INSTALL_TOOLCHAIN_ONLY
     "Only include toolchain files in the 'install' target." OFF)
   option(LLVM_FORCE_USE_OLD_HOST_TOOLCHAIN
@@ -235,9 +236,6 @@
   ${FLANG_SOURCE_DIR}/include/flang/Config/config.h.cmake
   ${FLANG_BINARY_DIR}/include/flang/Config/config.h)
 
-# Add global F18 flags.
-set(CMAKE_CXX_FLAGS "-fno-rtti -fno-exceptions -pedantic -Wall -Wextra -Werror -Wcast-qual -Wimplicit-fallthrough -Wdelete-non-virtual-dtor ${CMAKE_CXX_FLAGS}")
-
 # Builtin check_cxx_compiler_flag doesn't seem to work correctly
 macro(check_compiler_flag flag resultVar)
   unset(${resultVar} CACHE)
@@ -246,11 +244,11 @@
 
 check_compiler_flag("-Werror -Wno-deprecated-copy" CXX_SUPPORTS_NO_DEPRECATED_COPY_FLAG)
 if (CXX_SUPPORTS_NO_DEPRECATED_COPY_FLAG)
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-deprecated-copy")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-deprecated-copy")
 endif()
 check_compiler_flag("-Wstring-conversion" CXX_SUPPORTS_NO_STRING_CONVERSION_FLAG)
 if (CXX_SUPPORTS_NO_STRING_CONVERSION_FLAG)
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-string-conversion")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-string-conversion")
 endif()
 
 # Add appropriate flags for GCC
diff --git a/flang/unittests/Evaluate/CMakeLists.txt b/flang/unittests/Evaluate/CMakeLists.txt
--- a/flang/unittests/Evaluate/CMakeLists.txt
+++ b/flang/unittests/Evaluate/CMakeLists.txt
@@ -88,10 +88,12 @@
 # IEEE exception flags (different use of the word "exception")
 # in the actual hardware floating-point status register, so ensure that
 # C++ exceptions are enabled for this test.
-set_source_files_properties(real.cpp PROPERTIES COMPILE_FLAGS -fexceptions)
+set(LLVM_REQUIRES_EH ON)
+set(LLVM_REQUIRES_RTTI ON)
 add_executable(real-test
   real.cpp
 )
+llvm_update_compile_flags(real-test)
 
 target_link_libraries(real-test
   FortranEvaluateTesting
diff --git a/flang/unittests/Runtime/CMakeLists.txt b/flang/unittests/Runtime/CMakeLists.txt
--- a/flang/unittests/Runtime/CMakeLists.txt
+++ b/flang/unittests/Runtime/CMakeLists.txt
@@ -1,11 +1,12 @@
-if(CMAKE_COMPILER_IS_GNUCXX OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang"))
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
-endif()
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
 
+# RuntimeTesting needs exceptions enabled
+set(LLVM_REQUIRES_EH ON)
+set(LLVM_REQUIRES_RTTI ON)
 add_library(RuntimeTesting
   testing.cpp
   )
+llvm_update_compile_flags(RuntimeTesting)
 
 add_executable(format-test
   format.cpp