travis: Use a pre-installed jemalloc

Author: alexcrichton

.travis.yml

@@ -12,6 +12,7 @@ install:
   - sudo apt-get update -qq
   - sudo apt-get install -qq --force-yes -y llvm-$LLVM_VERSION
     llvm-${LLVM_VERSION}-dev clang-$LLVM_VERSION lldb-$LLVM_VERSION
+    libjemalloc-dev
 
 
 # All of the llvm tools are suffixed with "-$VERS" which we don't want, so
@@ -27,7 +28,8 @@ before_script:
   - ln -nsf /usr/bin/llvm-dis-$LLVM_VERSION local-llvm/bin/llvm-dis
   - ln -nsf /usr/bin/llc-$LLVM_VERSION local-llvm/bin/llc
   - ln -nsf /usr/include/llvm-$LLVM_VERSION local-llvm/include
-  - ./configure --disable-optimize-tests --llvm-root=`pwd`/local-llvm --enable-fast-make --enable-clang
+  - ./configure --disable-optimize-tests --llvm-root=`pwd`/local-llvm
+    --enable-fast-make --enable-clang --jemalloc-root=/usr/lib
 
 # Tidy everything up first, then build a few things, and then run a few tests.
 # Note that this is meant to run in a "fairly small" amount of time, so this