In travis-ci, build for osx also

Drop gcc b/c it takes too long to install via addon.

Build only static/release, to save VMs. (No shared to debug.)
diff --git a/travis.install.osx.sh b/travis.install.osx.sh
new file mode 100644
index 0000000..e82bdc6
--- /dev/null
+++ b/travis.install.osx.sh
@@ -0,0 +1,12 @@
+set -vex
+
+#brew update
+brew upgrade python3
+python3 -m venv venv
+source venv/bin/activate
+
+brew install ninja
+brew install meson
+
+#brew install pyenv
+#which pyenv