Use --sysroot when cross compiling.

As CMAKE_ROOT_FIND_PATH can be a list, a new CMAKE_SYSROOT is
introduced, which is never a list.

The contents of this variable is passed to supporting compilers
as --sysroot. It is also accounted for when processing implicit
link directories reported by the compiler, and when generating
RPATH information.
Add missing 'seen' check for evaluating COMPILE_OPTIONS.

Commit 089fe1c1 (Optimize genex evaluation for includes and
defines., 2013-02-01) introduced an optimization on DAG processing
to not reprocess properties on targets which have already been seen.

This was refactored slightly in commit 8dfdf1c7 (Fix the tests for
evaluating includes and defines., 2013-02-18), but was not extended
to cover COMPILE_OPTIONS in commit 80ca9c4b (Add COMPILE_OPTIONS target
property., 2013-05-16).

This omission causes the same performance regression in running
cmake on LLVM which 089fe1c1 fixed before, but this time for the
transitive evaluation of the COMPILE_OPTIONS property.
Find targets in INTERFACE_COMPILE_OPTIONS when exporting for try_compile.

This was missing from commit 80ca9c4b (Add COMPILE_OPTIONS target
property., 2013-05-16).
Use a preprocessor loop to manage the valid transitive properties.

Hopefully this will prevent regressions when adding further transitive
properties in the future.
QtAutomoc: Fix handling of list separator for compile definitions.
QtAutomoc: Use config-dependent compile definitions and includes.

Instead of always using the includes and defines which are not
config-specific, ensure that the config specific ones can be used.

Task-number: #13589
FindGTK2: Move check for pangocairo in gtk module
FindGTK2: Detect gthread library
FindX11: Search in /opt/X11 for OS X 10.8 (#14232)

As of Mac OS X 10.8, X11 is no longer installed under /usr/X11, but
under /opt/X11.
FindBoost: Clarify failure on missing 'static' libs (#14235)

When Boost_USE_STATIC_LIBS is ON we may complain that Boost libraries
cannot be found even when shared libraries are present.  Update the
error message to tell the user explicitly that we want static libraries.

Suggested-by: Laurence R. McGlashan <laurence.mcglashan@gmail.com>
OpenBSD: Enable ELF parsing and editing (#14241)

OpenBSD provides ELF ABI declarations in

 #include <stdint.h>
 #include <elf_abi.h>

Teach the platform check and cmELF implementation to use these.
CMakeDetermineVSServicePack: Improve documentation

Refer users to the newer CMAKE_<LANG>_COMPILER_VERSION variables.
Use a more concise summary.  Format the documentation to look
better in the "cmake --help-module" output.
CMakeDetermineVSServicePack: Add VS 11 update 1 and 2 (#14239)
Add whitespace after colons in error messages.
Merge topic 'FindGTK2-tweaks'

508e8ca FindGTK2: Detect gthread library
8dca8ce FindGTK2: Move check for pangocairo in gtk module
Merge topic 'FindX11-OSX-10.8'

488d968 FindX11: Search in /opt/X11 for OS X 10.8 (#14232)
Merge topic 'FindBoost-error-reason-static'

86cbd73 FindBoost: Clarify failure on missing 'static' libs (#14235)
Merge topic 'openbsd-elf-parsing'

480e924 OpenBSD: Enable ELF parsing and editing (#14241)
Merge topic 'CMakeDetermineVSServicePack-vs11'

2aa62e0 CMakeDetermineVSServicePack: Add VS 11 update 1 and 2 (#14239)
1746a35 CMakeDetermineVSServicePack: Improve documentation
Merge topic 'add-whitespace'

2331b57 Add whitespace after colons in error messages.