Switch all the macOS Travis jobs to use the Xcode 9 image.

We require Xcode 9 for the Swift target, and the C++ and .NET tests
shouldn't care either way.

We no longer need to install cmake: this is already in the Travis
Xcode 9.0 image (and it barfs if we try to install it again).

We no longer need the rvm bug workarounds; a newer version of rvm is
in the Xcode 9.0 image so this is no longer a problem.

The openssl package is already installed and up-to-date now, so there is
no need to install that.

These changes mean that we don't need before-install-osx-cpp.sh
or before-install-os-swift.sh at all, and before-install-osx-dotnet.sh
gets a bit shorter.  .travis.yml gets a small change to handle the
fact that some platform / target combos don't need before-install any more.

.travis.yml

@@ -67,42 +67,42 @@ matrix:
             - clang-3.7
     - os: osx
       compiler: clang
-      osx_image: xcode8.1
+      osx_image: xcode9
       env:
         - TARGET=cpp
         - GROUP=LEXER
       stage: extended-test
     - os: osx
       compiler: clang
-      osx_image: xcode8.1
+      osx_image: xcode9
       env:
         - TARGET=cpp
         - GROUP=PARSER
       stage: extended-test
     - os: osx
       compiler: clang
-      osx_image: xcode8.1
+      osx_image: xcode9
       env:
         - TARGET=cpp
         - GROUP=RECURSION
       stage: extended-test
     - os: osx
       compiler: clang
-      osx_image: xcode8.1
+      osx_image: xcode9
       env:
         - TARGET=swift
         - GROUP=LEXER
       stage: main-test
     - os: osx
       compiler: clang
-      osx_image: xcode8.1
+      osx_image: xcode9
       env:
         - TARGET=swift
         - GROUP=PARSER
       stage: main-test
     - os: osx
       compiler: clang
-      osx_image: xcode8.1
+      osx_image: xcode9
       env:
         - TARGET=swift
         - GROUP=RECURSION
@@ -114,19 +114,19 @@ matrix:
        - GROUP=ALL
       stage: extended-test
     - os: osx
-      osx_image: xcode8.2
+      osx_image: xcode9
       env:
         - TARGET=dotnet
         - GROUP=LEXER
       stage: extended-test
     - os: osx
-      osx_image: xcode8.2
+      osx_image: xcode9
       env:
         - TARGET=dotnet
         - GROUP=PARSER
       stage: extended-test
     - os: osx
-      osx_image: xcode8.2
+      osx_image: xcode9
       env:
         - TARGET=dotnet
         - GROUP=RECURSION
@@ -194,7 +194,7 @@ matrix:
       stage: main-test
 
 before_install:
-  - ./.travis/before-install-$TRAVIS_OS_NAME-$TARGET.sh
+  - f="./.travis/before-install-$TRAVIS_OS_NAME-$TARGET.sh"; ! [ -x "$f" ] || "$f"
 
 script:
   - cd runtime-testsuite; travis_wait 40 ../.travis/run-tests-$TARGET.sh

.travis/before-install-osx-cpp.sh

@@ -1,13 +0,0 @@
-#!/bin/bash
-
-set -euo pipefail
-
-thisdir=$(dirname "$0")
-
-brew update
-brew install cmake
-
-# Work around apparent rvm bug that is in Travis's Xcode image.
-# https://github.com/direnv/direnv/issues/210
-# https://github.com/travis-ci/travis-ci/issues/6307
-shell_session_update() { :; }

.travis/before-install-osx-dotnet.sh

@@ -4,9 +4,7 @@ set -euo pipefail
 
 thisdir=$(dirname "$0")
 
-# pre-requisites for dotnet core
-brew update
-brew install openssl
+# OpenSSL setup for dotnet core
 mkdir -p /usr/local/lib
 ln -s /usr/local/opt/openssl/lib/libcrypto.1.0.0.dylib /usr/local/lib/
 ln -s /usr/local/opt/openssl/lib/libssl.1.0.0.dylib /usr/local/lib/
@@ -19,9 +17,3 @@ sudo installer -pkg /tmp/dotnet-dev-osx-x64.1.0.4.pkg -target /
 
 # make the link
 ln -s /usr/local/share/dotnet/dotnet /usr/local/bin/
-
-# Work around apparent rvm bug that is in Travis's Xcode image.
-# https://github.com/direnv/direnv/issues/210
-# https://github.com/travis-ci/travis-ci/issues/6307
-shell_session_update() { :; }
-

.travis/before-install-osx-swift.sh

@@ -1,12 +0,0 @@
-#!/bin/bash
-
-set -euo pipefail
-
-thisdir=$(dirname "$0")
-
-brew update
-
-# Work around apparent rvm bug that is in Travis's Xcode image.
-# https://github.com/direnv/direnv/issues/210
-# https://github.com/travis-ci/travis-ci/issues/6307
-shell_session_update() { :; }