Fix typo for LLVM Directory.

This fixes the bootstrap script to use the proper LLVM dir for using the
proper clang version to compile Phasar.

Author: ddiepo-pjr

bootstrap.sh

@@ -120,8 +120,8 @@ ${DO_UNIT_TESTS} && echo "with unit tests."
 git submodule init
 git submodule update
 
-export CC=${LLVM_INSTALL}/bin/clang
-export CXX=${LLVM_INSTALL}/bin/clang++
+export CC=${LLVM_INSTALL_DIR}/bin/clang
+export CXX=${LLVM_INSTALL_DIR}/bin/clang++
 
 mkdir -p ${PHASAR_DIR}/build
 cd ${PHASAR_DIR}/build