travis: explicitly LD_LIBRARY_PATH the local libraries

Some of the libraries may be dlopened, which may not always work due to
the non-standard prefix that we're using.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Andres Gomez <agomez@igalia.com>

.travis.yml

@@ -36,6 +36,7 @@ env:
     - LLVM_PACKAGE="llvm-${LLVM_VERSION} llvm-${LLVM_VERSION}-dev"
     - LLVM_CONFIG="llvm-config-${LLVM_VERSION}"
     - PKG_CONFIG_PATH=$HOME/prefix/lib/pkgconfig
+    - LD_LIBRARY_PATH="$HOME/prefix/lib:$LD_LIBRARY_PATH"
     - MAKEFLAGS=-j2
   matrix:
     - BUILD=make