Help: Update CMAKE_SYSTEM* and CMAKE_HOST_SYSTEM* documentation

Update to documentation for HOST/TARGET system related variables to be
consistent with current functionality.

Help/variable/CMAKE_HOST_SYSTEM.rst

@@ -1,7 +1,10 @@
 CMAKE_HOST_SYSTEM
 -----------------
 
-Name of system cmake is being run on.
+Composit Name of OS CMake is being run on.
 
-The same as CMAKE_SYSTEM but for the host system instead of the target
-system when cross compiling.
+This variable is the composite of :variable:`CMAKE_HOST_SYSTEM_NAME` and
+:variable:`CMAKE_HOST_SYSTEM_VERSION`, e.g.
+``${CMAKE_HOST_SYSTEM_NAME}-${CMAKE_HOST_SYSTEM_VERSION}``.  If
+:variable:`CMAKE_HOST_SYSTEM_VERSION` is not set, then this variable is
+the same as :variable:`CMAKE_HOST_SYSTEM_NAME`.

Help/variable/CMAKE_HOST_SYSTEM_NAME.rst

@@ -3,5 +3,6 @@ CMAKE_HOST_SYSTEM_NAME
 
 Name of the OS CMake is running on.
 
-The same as CMAKE_SYSTEM_NAME but for the host system instead of the
-target system when cross compiling.
+On systems that have the uname command, this variable is set to the
+output of uname -s.  ``Linux``, ``Windows``, and ``Darwin`` for Mac OS X
+are the values found on the big three operating systems.

Help/variable/CMAKE_HOST_SYSTEM_PROCESSOR.rst

@@ -3,5 +3,6 @@ CMAKE_HOST_SYSTEM_PROCESSOR
 
 The name of the CPU CMake is running on.
 
-The same as CMAKE_SYSTEM_PROCESSOR but for the host system instead of
-the target system when cross compiling.
+On systems that support uname, this variable is set to the output of
+uname -p, on windows it is set to the value of the environment variable
+``PROCESSOR_ARCHITECTURE``.

Help/variable/CMAKE_HOST_SYSTEM_VERSION.rst

@@ -1,7 +1,8 @@
 CMAKE_HOST_SYSTEM_VERSION
 -------------------------
 
-OS version CMake is running on.
+The OS version CMake is running on.
 
-The same as CMAKE_SYSTEM_VERSION but for the host system instead of
-the target system when cross compiling.
+A numeric version string for the system.  On systems that support
+uname, this variable is set to the output of uname -r. On other
+systems this is set to major-minor version numbers.

Help/variable/CMAKE_SYSTEM.rst

@@ -1,9 +1,10 @@
 CMAKE_SYSTEM
 ------------
 
-Name of system cmake is compiling for.
+Composit Name of OS CMake is compiling for.
 
-This variable is the composite of CMAKE_SYSTEM_NAME and
-CMAKE_SYSTEM_VERSION, like this
-${CMAKE_SYSTEM_NAME}-${CMAKE_SYSTEM_VERSION}.  If CMAKE_SYSTEM_VERSION
-is not set, then CMAKE_SYSTEM is the same as CMAKE_SYSTEM_NAME.
+This variable is the composite of :variable:`CMAKE_SYSTEM_NAME` and
+:variable:`CMAKE_SYSTEM_VERSION`, e.g.
+``${CMAKE_SYSTEM_NAME}-${CMAKE_SYSTEM_VERSION}``.  If
+:variable:`CMAKE_SYSTEM_VERSION` is not set, then this variable is
+the same as :variable:`CMAKE_SYSTEM_NAME`.

Help/variable/CMAKE_SYSTEM_NAME.rst

@@ -3,7 +3,6 @@ CMAKE_SYSTEM_NAME
 
 Name of the OS CMake is building for.
 
-This is the name of the operating system on which CMake is targeting.
-On systems that have the uname command, this variable is set to the
-output of uname -s.  Linux, Windows, and Darwin for Mac OS X are the
-values found on the big three operating systems.
+This is the name of the OS on which CMake is targeting.  This variable
+is the same as :variable:`CMAKE_HOST_SYSTEM_NAME` if you build for the
+host system instead of the target system when cross compiling.

Help/variable/CMAKE_SYSTEM_PROCESSOR.rst

@@ -3,6 +3,6 @@ CMAKE_SYSTEM_PROCESSOR
 
 The name of the CPU CMake is building for.
 
-On systems that support uname, this variable is set to the output of
-uname -p, on windows it is set to the value of the environment
-variable PROCESSOR_ARCHITECTURE
+This variable is the same as :variable:`CMAKE_HOST_SYSTEM_PROCESSOR` if
+you build for the host system instead of the target system when
+cross compiling.

Help/variable/CMAKE_SYSTEM_VERSION.rst

@@ -1,8 +1,8 @@
 CMAKE_SYSTEM_VERSION
 --------------------
 
-OS version CMake is building for.
+The OS version CMake is building for.
 
-A numeric version string for the system, on systems that support
-uname, this variable is set to the output of uname -r.  On other
-systems this is set to major-minor version numbers.
+This variable is the same as :variable:`CMAKE_HOST_SYSTEM_VERSION` if
+you build for the host system instead of the target system when
+cross compiling.