Use g++ 4.8 on YouCompleteMe builds too as the new boost requires this

.travis.yml

@@ -11,6 +11,9 @@ install:
 script:
   - ci/travis/travis_script.sh
 env:
+  global:
+    # Travis can run out of RAM, so we need to be careful here.
+    - YCM_CORES=3
   matrix:
     - YCM_PYTHON_VERSION=2.7 YCM_FLAKE8=true
     # Since 3.0.4, Flake8 is not working anymore on Python 2.6.
@@ -30,6 +33,7 @@ addons:
     packages:
      - cmake-data
      - cmake
+     - g++-4.8
      - ninja-build
      # Everything below is a Python build dep (though it depends on Python
      # version). We need them because pyenv builds Python.

ci/travis/travis_install.linux.sh

@@ -1,5 +1,15 @@
 # Linux-specific installation
 
+# We can't use sudo, so we have to approximate the behaviour of setting the
+# default system compiler.
+
+mkdir ${HOME}/bin
+
+ln -s /usr/bin/g++-4.8 ${HOME}/bin/c++
+ln -s /usr/bin/gcc-4.8 ${HOME}/bin/cc
+
+export PATH=${HOME}/bin:${PATH}
+
 # In order to work with ycmd, python *must* be built as a shared library. This
 # is set via the PYTHON_CONFIGURE_OPTS option.
 export PYTHON_CONFIGURE_OPTS="--enable-shared"