add Travis llvm test

.travis.yml

@@ -12,6 +12,8 @@ env:
     - SYMPY_SRC=sympy-1.0
     - DOC="false"
     - PYPY_NUMPY="false"
+    - LLVM="false"
+    - LLVM_VERSION=3.8.0
   matrix:
     - CYTHON="false"
     - CYTHON="true"
@@ -22,6 +24,8 @@ matrix:
       env: DOC="true" CYTHON="false"
     - python: 3.5
       env: DOC="true" CYTHON="false"
+    - python: 3.5
+      env: LLVM="true" CYTHON="false"
     - python: 2.7
       env: SYMPY_SRC=master CYTHON="false"
     - python: 3.5
@@ -40,6 +44,9 @@ matrix:
     - env: SYMPY_SRC=master CYTHON="false"
     - env: DOC="true" CYTHON="false"
     - env: PYPY_NUMPY="true"
+cache:
+  directories:
+    - llvm-3.8.0
 before_install:
   - "export DISPLAY=:99.0"
   - "sh -e /etc/init.d/xvfb start"
@@ -50,6 +57,17 @@ before_install:
   - if [[ "$CYTHON" == "true" ]]; then
       pip install cython;
     fi
+  - if [[ "$LLVM" == "true" ]]; then
+      if [ -z "$(ls -A llvm-$LLVM_VERSION)" ]; then
+        wget -O llvm-$LLVM_VERSION.tar.xz http://llvm.org/releases/$LLVM_VERSION/clang+llvm-$LLVM_VERSION-x86_64-linux-gnu-ubuntu-14.04.tar.xz;
+        mkdir llvm-$LLVM_VERSION;
+        xzcat llvm-$LLVM_VERSION.tar.xz | tar -xvf - --strip 1 -C llvm-$LLVM_VERSION;
+      fi;
+      sudo apt-get install libstdc++6;
+      llvm-$LLVM_VERSION/bin/llvm-config --version;
+      export LLVM_CONFIG="llvm-$LLVM_VERSION/bin/llvm-config";
+      pip install llvmlite;
+    fi
   - pip install unittest2
   - pip install pexpect
   - pip install git+https://github.com/sympy/sympy.git@$SYMPY_SRC