Adding LLVM src downloading script

llvm/tools/hpvm/llvm_installer/llvm_installer.sh

+#!/bin/bash
+
+VERSION="9.0.0"
+
+URL="http://releases.llvm.org"
+ 
+SUFFIX=".tar.xz"
+LLVM_SRC="llvm-$VERSION.src"
+
+WGET=wget
+
+CURRENT_DIR=`pwd`
+INSTALL_DIR=`pwd`/install
+BUILD_DIR=$CURRENT_DIR/$LLVM_SRC/build
+
+NUM_THREADS=12
+
+if [ -d $LLVM_SRC ]; then
+    echo Found $LLVM_SRC!
+else
+    echo $WGET $URL/$VERSION/$LLVM_SRC$SUFFIX
+    $WGET $URL/$VERSION/$LLVM_SRC$SUFFIX
+    tar xf $LLVM_SRC$SUFFIX
+fi
+
+cd $CURRENT_DIR
+
+if [ -d $BUILD_DIR ]; then
+    cd $BUILD_DIR
+    echo Found $BUILD_DIR.
+else
+    mkdir -p $BUILD_DIR
+    mkdir -p $INSTALL_DIR
+    cd $BUILD_DIR
+    cmake -DCMAKE_BUILD_TYPE=MinSizeRel -DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++ -DCMAKE_INSTALL_PREFIX=$INSTALL_DIR -DLLVM_OPTIMIZED_TABLEGEN=On  ..
+fi
+
+make -j$NUM_THREADS
+make install
+
+if [ -x $INSTALL_DIR/bin/clang ]; then
+    true
+else
+    echo LLVM not installed properly.
+    exit 0
+fi
+
+cd $CURRENT_DIR
+echo "Add $INSTALL_DIR/bin to PATH variable."
+export PATH="$INSTALL_DIR/bin:$PATH"
+
+