Tweaked minimum clang versions; added minimum requirements notes

CMakeLists.txt

@@ -321,17 +321,17 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND
 endif ()
 
 #-----------------------------------------------------------------------------
-# Minimum compiler version check: LLVM Clang >= 2.8
+# Minimum compiler version check: LLVM Clang >= 3.0
 if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 2.8)
-  message(FATAL_ERROR "LLVM Clang 2.8 or later is required.")
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.0)
+  message(FATAL_ERROR "LLVM Clang 3.0 or later is required.")
 endif ()
 
 #-----------------------------------------------------------------------------
-# Minimum compiler version check: Apple Clang >= 2.0 (Xcode 4.0.x)
+# Minimum compiler version check: Apple Clang >= 3.0 (Xcode 4.2)
 if (CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" AND
-    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 2.0)
-  message(FATAL_ERROR "Apple Clang 2.0 or later is required.")
+    CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.0)
+  message(FATAL_ERROR "Apple Clang 3.0 or later is required.")
 endif ()
 
 #-----------------------------------------------------------------------------

README.md

@@ -57,6 +57,23 @@ If you have found a bug:
 
 [VTK Issue Tracker]: http://www.vtk.org/Bug
 
+Requirements
+============
+
+In general VTK tries to be as portable as possible; the specific configurations below are known to work and tested.
+
+VTK supports the following compilers:
+1. Microsoft Visual Studio 2008 (aka MSVC++ 9.0) or newer
+2. gcc 4.2 or newer
+3. Apple gcc 4.2 (from Xcode 3.1.4 or newer)
+4. Clang 3.0 or newer
+5. Apple Clang 3.0 (from Xcode 4.2) or newer
+
+VTK supports the following operating systems:
+1. Windows Vista or newer
+2. Mac OS X 10.6.8 or newer
+3. Linux (ex: Ubuntu 12.04 or newer, Debian 4 or newer)
+
 Contributing
 ============