Xcode: Add CMAKE_XCODE_SCHEME_ENVIRONMENT variable

Initialize the `XCODE_SCHEME_ENVIRONMENT` target property.

This was left out of commit 6b7f1e1db0 (Xcode: Add variables and
properties to configure schemes, 2018-07-29, v3.13.0-rc1~243^2).

Help/manual/cmake-variables.7.rst

@@ -241,6 +241,7 @@ Variables that Change Behavior
    /variable/CMAKE_XCODE_SCHEME_DISABLE_MAIN_THREAD_CHECKER
    /variable/CMAKE_XCODE_SCHEME_DYNAMIC_LIBRARY_LOADS
    /variable/CMAKE_XCODE_SCHEME_DYNAMIC_LINKER_API_USAGE
+   /variable/CMAKE_XCODE_SCHEME_ENVIRONMENT
    /variable/CMAKE_XCODE_SCHEME_GUARD_MALLOC
    /variable/CMAKE_XCODE_SCHEME_MAIN_THREAD_CHECKER_STOP
    /variable/CMAKE_XCODE_SCHEME_MALLOC_GUARD_EDGES

Help/release/dev/xcode-scheme-env.rst

@@ -0,0 +1,5 @@
+xcode-scheme-env
+----------------
+
+* The :variable:`CMAKE_XCODE_SCHEME_ENVIRONMENT` variable was added
+  to initialize the :prop_tgt:`XCODE_SCHEME_ENVIRONMENT` target property.

Help/variable/CMAKE_XCODE_SCHEME_ENVIRONMENT.rst

@@ -0,0 +1,15 @@
+CMAKE_XCODE_SCHEME_ENVIRONMENT
+------------------------------
+
+Specify environment variables that should be added to the Arguments
+section of the generated Xcode scheme.
+
+If set to a list of environment variables and values of the form
+``MYVAR=value`` those environment variables will be added to the
+scheme.
+
+This variable initializes the :prop_tgt:`XCODE_SCHEME_ENVIRONMENT`
+property on all targets.
+
+Please refer to the :prop_tgt:`XCODE_GENERATE_SCHEME` target property
+documentation to see all Xcode schema related properties.

Source/cmTarget.cxx

@@ -380,6 +380,7 @@ cmTarget::cmTarget(std::string const& name, cmStateEnums::TargetType type,
       initProp("XCODE_SCHEME_MALLOC_STACK");
       initProp("XCODE_SCHEME_DYNAMIC_LINKER_API_USAGE");
       initProp("XCODE_SCHEME_DYNAMIC_LIBRARY_LOADS");
+      initProp("XCODE_SCHEME_ENVIRONMENT");
     }
 #endif
   }