CMake: set OSX specific variables properly

On OSX 10.10, one gets errors of the type:

[cmake] CMake Error at Modules/Platform/Darwin.cmake:76 (message):
[cmake]   CMAKE_OSX_DEPLOYMENT_TARGET is '10.10' but CMAKE_OSX_SYSROOT:
[cmake]
[cmake]    ""
[cmake]
[cmake]   is not set to a MacOSX SDK with a recognized version.  Either set
[cmake]   CMAKE_OSX_SYSROOT to a valid SDK or set CMAKE_OSX_DEPLOYMENT_TARGET to
[cmake]   empty.
[cmake] Call Stack (most recent call first):
[cmake]   Modules/CMakeSystemSpecificInformation.cmake:36 (include)
[cmake]   CMakeLists.txt:16 (project)

Unless the CMAKE_OSX_DEPLOYMENT_TARGET is set to empty. We set it to empty by
unsetting the MACOSX_DEPLOYMENT_TARGET environment variable.

Similar problem happens when cmake is used to build other packages. There the
fix is to unset the CMAKE_OSX_DEPLOYMENT_TARGET variable on the command line.

Author: certik

base/cmake_package.py

@@ -34,6 +34,9 @@ def configure(ctx, stage_args):
     else:
         conf_lines.append('-DCMAKE_BUILD_TYPE:STRING=Release')
 
+    if ctx.parameters['platform'] == 'Darwin':
+        conf_lines.append('-DCMAKE_OSX_DEPLOYMENT_TARGET:STRING=""')
+
     #cmake needs to be given all the dependency dirs as prefix paths
     #so that we search the hashdist directories before the system directories
     #CMake doesn't use the CPPFLAGS implicitly to find libraries

pkgs/cmake.yaml

@@ -8,6 +8,14 @@ sources:
   url: http://www.cmake.org/files/v3.2/cmake-3.2.2.tar.gz
 
 build_stages:
+- when: platform == 'Darwin'
+  name: fix_deployment_target
+  after: prologue
+  before: configure
+  handler: bash
+  bash: |
+    unset MACOSX_DEPLOYMENT_TARGET
+
 - name: configure
   extra: ['--parallel=${HASHDIST_CPU_COUNT}',
           '--system-bzip2',