Build FirebaseCore from CMake (#594)

* Don't bother specifying a download directory to CMake ExternalProject
* Teach CMake to build pure Xcode projects as dependencies

  This allows downstream code (like log_apple.mm) to consume this for
  testing within the CMake build without requiring a CMake-native build
  for these components.

  This makes integrating these components into the cmake build essentially
  free from the point of view of the consumed component.

* Get the CMake build semi-working on Linux again

  Many prebuilt versions of cmake on Linux lack the ability to download
  over https so use git to get googletest.

  Don't attempt to build FirebaseCore on Linux; there's no xcodebuild.

  Note the build is still ultimately broken because we don't yet have an
  alternative to arc4random on Linux but at least this is no more broken
  than it was before.

1 files changed, 23 insertions, 0 deletions

diff --git a/cmake/external/FirebaseCore.cmake b/cmake/external/FirebaseCore.cmake
new file mode 100644
index 0000000..8be6969
--- /dev/null
+++ b/cmake/external/FirebaseCore.cmake
@@ -0,0 +1,23 @@
+# Copyright 2017 Google
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+include(xcodebuild)
+
+if(APPLE)
+  # FirebaseCore is only available as a CocoaPod build.
+  xcodebuild(FirebaseCore)
+else()
+  # On non-Apple platforms, there's no way to build FirebaseCore.
+  add_custom_target(FirebaseCore)
+endif()