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.