Confusing as it may be, we need LLVM_ENABLE_WARNINGS=ON to turn warnings off.

ROOT will add -Wall; llvm only suppressed warnings if they are on.

interpreter/CMakeLists.txt

 
 #---Define the way we want to build and what of llvm/clang/cling------------------------------------
-set(LLVM_ENABLE_WARNINGS OFF CACHE BOOL "")
+set(LLVM_ENABLE_WARNINGS ON CACHE BOOL "")
 set(LLVM_INCLUDE_TESTS OFF CACHE BOOL "")
 set(LLVM_INCLUDE_EXAMPLES OFF CACHE BOOL "")
 set(LLVM_BUILD_TOOLS OFF CACHE BOOL "")

interpreter/llvm/Module.mk

@@ -188,7 +188,7 @@ $(LLVMDEPO): $(LLVMDEPS)
 		-DCMAKE_INSTALL_PREFIX=$(ROOT_OBJDIR)/$(LLVMDIRI) \
 		-DLLVM_BUILD_DOCS=OFF \
 		-DLLVM_BUILD_TESTS=OFF \
-		-DLLVM_ENABLE_WARNINGS=OFF \
+		-DLLVM_ENABLE_WARNINGS=ON \
 		-DLLVM_INCLUDE_TESTS=OFF \
 		-DLLVM_INCLUDE_EXAMPLES=OFF \
 		-DLLVM_FORCE_USE_OLD_TOOLCHAIN=ON \