Adding check for broken version of Clang with Xcode 4.5.x.

- Also updating EXECUTE_PROCESS() calls to compiler to handle case
  when a compilation wrapper (e.g. ccache) is used.

Change-Id: I32837233a06ed1843125fb04852f82a9b8503769

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 982453b..cb022ca 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -456,7 +456,10 @@
       SET (CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -msse3")
       # Use of -fast only applicable for Apple's GCC
       # Assume this is being used if GCC version < 4.3 on OSX
-      EXECUTE_PROCESS(COMMAND ${CMAKE_C_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION)
+      EXECUTE_PROCESS(COMMAND ${CMAKE_C_COMPILER}
+        ARGS ${CMAKE_CXX_COMPILER_ARG1} -dumpversion
+        OUTPUT_VARIABLE GCC_VERSION
+        OUTPUT_STRIP_TRAILING_WHITESPACE)
       IF (GCC_VERSION VERSION_LESS 4.3)
         SET (CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -fast")
       ENDIF (GCC_VERSION VERSION_LESS 4.3)
@@ -533,6 +536,24 @@
   ENDIF(HAVE_RETURN_TYPE_C_LINKAGE)
 ENDIF ()
 
+# Xcode 4.5.x used Clang 4.1 (Apple version), this has a bug that prevents
+# compilation of Ceres.
+IF (APPLE AND CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+  EXECUTE_PROCESS(COMMAND ${CMAKE_CXX_COMPILER}
+    ARGS ${CMAKE_CXX_COMPILER_ARG1} -dumpversion
+    OUTPUT_VARIABLE CLANG_VERSION
+    OUTPUT_STRIP_TRAILING_WHITESPACE)
+  # Use version > 4.0 & < 4.2 to catch all 4.1(.x) versions.
+  IF (CLANG_VERSION VERSION_GREATER 4.0 AND
+      CLANG_VERSION VERSION_LESS 4.2)
+    MESSAGE(FATAL_ERROR "You are attempting to build Ceres on OS X using Xcode "
+      "4.5.x (Clang version: ${CLANG_VERSION}). This version of Clang has a "
+      "bug that prevents compilation of Ceres, please update to "
+      "Xcode >= 4.6.3.")
+  ENDIF (CLANG_VERSION VERSION_GREATER 4.0 AND
+    CLANG_VERSION VERSION_LESS 4.2)
+ENDIF (APPLE AND CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+
 ADD_SUBDIRECTORY(internal/ceres)
 
 IF (BUILD_DOCUMENTATION)

docs/source/building.rst

diff --git a/docs/source/building.rst b/docs/source/building.rst
index 38a539b..49fdb3c 100644
--- a/docs/source/building.rst
+++ b/docs/source/building.rst
@@ -192,6 +192,12 @@
 <https://developer.apple.com/library/mac/#documentation/Performance/Conceptual/vecLib/Reference/reference.html>`_
 framework.
 
+.. NOTE::
+
+ Ceres will not compile using Xcode 4.5.x (Clang version 4.1) due to a bug in that version of
+ Clang.  If you are running Xcode 4.5.x, please update to Xcode >= 4.6.x before attempting to
+ build Ceres.
+
 .. code-block:: bash
 
       # CMake