Fix clang warnings

.travis/build-linux.bash

@@ -25,6 +25,7 @@ if [ $COMPILER = "gcc" ]; then
 	# We need to set the following variables for LTO to link properly
 	export AR=/usr/bin/gcc-ar-9
 	export RANLIB=/usr/bin/gcc-ranlib-9
+	export CFLAGS="-fuse-linker-plugin"
 else
 	export CC=${CLANG_BINARY}
 	export CXX=${CLANGXX_BINARY}
@@ -33,7 +34,7 @@ else
 	export RANLIB=/usr/bin/llvm-ranlib-$LLVMVER
 fi
 
-export CFLAGS="-fuse-linker-plugin -fuse-ld=${LINKER}"
+export CFLAGS="$CFLAGS -fuse-ld=${LINKER}"
 
 cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DBUILD_LLVM_SUBMODULE=OFF -DUSE_COTIRE=OFF -DLLVM_DIR=llvmlibs/lib/cmake/llvm/ -DUSE_NATIVE_INSTRUCTIONS=OFF \
   -DCMAKE_C_FLAGS="$CFLAGS" -DCMAKE_CXX_FLAGS="$CFLAGS" -DCMAKE_AR=$AR -DCMAKE_RANLIB=$RANLIB \