Travis: cache Yosys installation explicitly.

.travis.yml

@@ -6,11 +6,13 @@ python:
 cache:
   directories:
     - "$HOME/.ccache"
+    - "$HOME/.local"
 before_install:
-  - export PATH="/usr/lib/ccache:$PATH"
+  - export PATH="/usr/lib/ccache:$HOME/.local/bin:$PATH"
 install:
   - pip install coverage codecov pyvcd
-  - git clone https://github.com/YosysHQ/yosys && (cd yosys && make CONFIG=gcc ENABLE_ABC=0)
+  - git clone https://github.com/YosysHQ/yosys
+  - (cd yosys && if ! yosys -V || [ $(git rev-parse HEAD $(yosys -V | awk 'match($0,/sha1 ([0-9a-f]+)/,m) { print m[1] }') | uniq | wc -l) != 1 ]; then make CONFIG=gcc ENABLE_ABC=0 PREFIX=$HOME/.local install; fi)
 script:
   - coverage run -m unittest discover
   - codecov