OS X: Link with all framework search paths, not just the last

Refactoring in commit 8d674e78 (Ninja: move -LIBPATH behind -link
option, 2012-09-26) accidentally added code that overwrites the
framework search path flags on each iteration instead of appending.
Change '=' to '+=' to fix it.  This affects Makefile and Ninja
generators.
OS X: Detect implicit link directories on modern toolchains

We detect the implicit link directories for the toolchain by adding a
flag to get verbose output from the compiler front-end while linking the
ABI detection binary.  Newer OS X toolchains based on Clang do not add
the implicit link directories with -L options to their internal
invocation of "ld".  Instead they use a linker that comes with the
toolchain and is already configured with the proper directories.

Add the "-Wl,-v" option to ask "ld" to print its implicit directories.
It displays them in a block such as:

 Library search paths:
	/...

Parse this block to extract the implicit link directories.

While at it, remove the checks introduced by commit efaf335b (Skip
implicit link information on Xcode, 2009-07-23) and commit 5195a664
(Skip implicit link info for multiple OS X archs, 2009-09-22).  Discard
the non-system link directories added by Xcode.  Discard all detected
implicit libraries in the multi-architecture case but keep the
directories.  The directories are still useful without the libraries
just to suppress addition of explicit -L options for them.
OS X: Detect implicit linker framework search paths

Previously we hard-coded a list of implicit framework directories but
did not account for CMAKE_OSX_SYSROOT or for changes to the list across
OS X versions.  Instead we should automatically detect the framework
directories for the active toolchain.

The parent commit added the "-Wl,-v" option to ask "ld" to print its
implicit directories.  It displays a block such as:

 Framework search paths:
	/...

Parse this block to extract the list of framework directories.

Detection may fail on toolchains that do not list their framework
directories, such as older OS X linkers.  Always treat the paths

 <sdk>/Library/Frameworks
 <sdk>/System/Library/Frameworks
 <sdk>/Network/Library/Frameworks # Older OS X only
 /System/Library/Frameworks

as implicit.  Note that /System/Library/Frameworks should always be
considered implicit so that frameworks CMake finds there will not
override the SDK copies.
Don't crash when a target is expected but is not available.
add_library: Document object library portability suggestion

Xcode and VS <= 7.1 will not build targets that have no source files
besides $<TARGET_OBJECTS:...>.  Suggest in the documentation that
projects always add at least one real source file.
GenEx: Add expressions to specify build- or install-only values

This is for specifying INCLUDE_DIRECTORIES relevant to the build-location
or the install location for example:

 set_property(TARGET foo PROPERTY
   INTERFACE_INCLUDE_DIRECTORIES
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR};${CMAKE_CURRENT_SOURCE_DIR}>"
   "$<INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/include>"
 )

A 'bar' target can then use:

 set_property(TARGET bar PROPERTY
   INCLUDE_DIRECTORIES
   "$<TARGET_PROPERTY:foo,INTERFACE_INCLUDE_DIRECTORIES>"
 )

and it will work whether foo is in the same project, or an imported target
from an installation location, or an imported target from a build location
generated by the export() command.

Because the generator expressions are only evaluated at build-time, these
new expressions are equivalent to the ZeroNode and OneNode.

The GeneratorExpression test is split into parts. Some shells can't run
the custom command as it is getting too long.
Allow generator expressions to require literals.
Add the TARGET_NAME generator expression.

It will be used as a preprocessing marker.
Add API to extract target names from a genex string.

The TARGET_NAME expression, which requires a literal, provides
target names. $<TARGET_PROPERTY:tgt,prop> also provides target
names in the cases where tgt is a literal, so that TARGET_NAME is
not needed then in addition.
Add API to populate INTERFACE properties in exported targets.

The INTERFACE properties need to be preprocessed for context (build
location or install location) and to extract target names etc.
Make all relevant targets available in the genex context.

The current node being evaluated transitively in the generator
expression must be available to resolve mapped configs.
Use mapped config properties to evaluate $<CONFIG>
Make cycles in target properties ignored, not an error.

Constructs such as these are an error as they are direct self-references:

 set_property(TARGET foo APPEND PROPERTY
   INCLUDE_DIRECTORIES $<TARGET_PROPERTY:foo,INCLUDE_DIRECTORIES>)
 set_property(TARGET foo APPEND PROPERTY
   INCLUDE_DIRECTORIES $<TARGET_PROPERTY:INCLUDE_DIRECTORIES>)

However, this is an indirect self-reference in a cycle, and not an error:

 set_property(TARGET foo APPEND PROPERTY
   INCLUDE_DIRECTORIES $<TARGET_PROPERTY:bar,INCLUDE_DIRECTORIES>)
 set_property(TARGET bar APPEND PROPERTY
   INCLUDE_DIRECTORIES $<TARGET_PROPERTY:foo,INCLUDE_DIRECTORIES>)
Populate the ExportedTargets member early in GenerateMainFile

The member variable is checked to determine whether to call
HandleMissingTarget(). As that could be called during the loop in
the comming commits, ensure that it contains all targets being
exported.
Handle INTERFACE properties transitively for includes and defines.

Contextually, the behavior is as if the properties content from another
target is included in the string and then the result is evaluated.
Ninja: fix building from Codeblocks GUI

Many thx to Chuck Frayman

BUG: 13652
Qt4: Add module dependencies to the IMPORTED targets

This means for example, that consumers can use:

 target_link_libraries(foo ${QT_QTGUI_LIBRARIES})

instead of also needing to specify all 'public' dependencies:

 target_link_libraries(foo ${QT_QTGUI_LIBRARIES} ${QT_QTCORE_LIBRARIES} )

when using the IMPORTED targets.  Also populate the
IMPORTED_LINK_DEPENDENT_LIBRARIES property so CMake can help the linker
find shared library dependencies.
Add test for custom command with a genex referring to a target.

This test failed before d8a59ea4 (Port cmGeneratorExpression to
cmTarget from cmGeneratorTarget, 2012-10-27), and passes after.
Merge topic 'qt4-target-depends'

57a67bf Qt4: Add module dependencies to the IMPORTED targets
Merge topic 'fix-genex-with-no-target'

e767ffc Don't crash when a target is expected but is not available.