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.

1 files changed, 9 insertions, 0 deletions

diff --git a/Source/cmDocumentVariables.cxx b/Source/cmDocumentVariables.cxx
index 55d70f8..0a4170b 100644
--- a/Source/cmDocumentVariables.cxx
+++ b/Source/cmDocumentVariables.cxx
@@ -1625,6 +1625,15 @@ void cmDocumentVariables::DefineVariables(cmake* cm)
      "Variables for Languages");
 
   cm->DefineProperty
+    ("CMAKE_<LANG>_IMPLICIT_LINK_FRAMEWORK_DIRECTORIES", cmProperty::VARIABLE,
+     "Implicit linker framework search path detected for language <LANG>.",
+     "These paths are implicit linker framework search directories for "
+     "the compiler's language.  "
+     "CMake automatically detects these directories for each language and "
+     "reports the results in this variable.", false,
+     "Variables for Languages");
+
+  cm->DefineProperty
     ("CMAKE_<LANG>_IMPLICIT_LINK_LIBRARIES", cmProperty::VARIABLE,
      "Implicit link libraries and flags detected for language <LANG>.",
      "Compilers typically pass language runtime library names and "