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.

1 files changed, 9 insertions, 12 deletions

diff --git a/Modules/CMakeDetermineCompilerABI.cmake b/Modules/CMakeDetermineCompilerABI.cmake
index 75247d9..cb94aa6 100644
--- a/Modules/CMakeDetermineCompilerABI.cmake
+++ b/Modules/CMakeDetermineCompilerABI.cmake
@@ -72,18 +72,7 @@ function(CMAKE_DETERMINE_COMPILER_ABI lang src)
       # Parse implicit linker information for this language, if available.
       set(implicit_dirs "")
       set(implicit_libs "")
-      set(MULTI_ARCH FALSE)
-      if(DEFINED CMAKE_OSX_ARCHITECTURES)
-        if( "${CMAKE_OSX_ARCHITECTURES}" MATCHES ";" )
-          set(MULTI_ARCH TRUE)
-        endif()
-      endif()
-      if(CMAKE_${lang}_VERBOSE_FLAG
-          # Implicit link information cannot be used explicitly for
-          # multiple OS X architectures, so we skip it.
-          AND NOT MULTI_ARCH
-          # Skip this with Xcode for now.
-          AND NOT "${CMAKE_GENERATOR}" MATCHES Xcode)
+      if(CMAKE_${lang}_VERBOSE_FLAG)
         CMAKE_PARSE_IMPLICIT_LINK_INFO("${OUTPUT}" implicit_libs implicit_dirs log
           "${CMAKE_${lang}_IMPLICIT_OBJECT_REGEX}")
         file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
@@ -112,6 +101,14 @@ function(CMAKE_DETERMINE_COMPILER_ABI lang src)
         message(STATUS "${_desc}")
       endif()
 
+      # Implicit link libraries cannot be used explicitly for multiple
+      # OS X architectures, so we skip it.
+      if(DEFINED CMAKE_OSX_ARCHITECTURES)
+        if("${CMAKE_OSX_ARCHITECTURES}" MATCHES ";")
+          set(implicit_libs "")
+        endif()
+      endif()
+
       set(CMAKE_${lang}_IMPLICIT_LINK_LIBRARIES "${implicit_libs}" PARENT_SCOPE)
       set(CMAKE_${lang}_IMPLICIT_LINK_DIRECTORIES "${implicit_dirs}" PARENT_SCOPE)