Try setting CMAKE_PREFIX_PATH to llvm-7 tree in test_travis.sh

bin/install_travis.sh

@@ -106,7 +106,6 @@ if [[ ! -z "${WITH_LLVM}" ]]; then
     export LLVM_DIR=$our_install_dir/share/llvm/
 elif [[ ! -z "${WITH_SANITIZE}" ]]; then
     export LLVM_DIR=/usr/lib/llvm-7/share/llvm/
-    export CMAKE_PREFIX_PATH=/usr/lib/llvm-7
     export CC=clang-7
     export CXX=clang++-7
 fi

bin/test_travis.sh

@@ -20,6 +20,9 @@ pwd
 echo "Running cmake:"
 # We build the command line here. If the variable is empty, we skip it,
 # otherwise we pass it to cmake.
+if [[ ! -z "${WITH_SANITIZE}" ]]; then
+    export CMAKE_PREFIX_PATH=/usr/lib/llvm-7
+fi
 cmake_line="-DCMAKE_INSTALL_PREFIX=$our_install_dir -DCMAKE_PREFIX_PATH=$our_install_dir:${CMAKE_PREFIX_PATH}"
 if [[ "${BUILD_TYPE}" != "" ]]; then
     cmake_line="$cmake_line -DCMAKE_BUILD_TYPE=${BUILD_TYPE}"