[cmake] Check the compiler version first

Otherwise users get messages from CheckAtomic about missing libatomic
instead of a sensible message that says "use GCC 4.7 or newer".

I structured the change along the lines of HandleLLVMStdlib.cmake, so
that the standalone build of Clang still gets the compiler version
check.

Reviewers: beanz

Differential Revision: http://reviews.llvm.org/D17789

llvm-svn: 262491
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 757042c..7036e74 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -6,54 +6,12 @@
 # else.
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 
+include(CheckCompilerVersion)
 include(HandleLLVMStdlib)
 include(AddLLVMDefinitions)
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 
-if(NOT LLVM_FORCE_USE_OLD_TOOLCHAIN)
-  if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.7)
-      message(FATAL_ERROR "Host GCC version must be at least 4.7!")
-    endif()
-  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.1)
-      message(FATAL_ERROR "Host Clang version must be at least 3.1!")
-    endif()
-
-    if (CMAKE_CXX_SIMULATE_ID MATCHES "MSVC")
-      if (CMAKE_CXX_SIMULATE_VERSION VERSION_LESS 18.0)
-        message(FATAL_ERROR "Host Clang must have at least -fms-compatibility-version=18.0")
-      endif()
-      set(CLANG_CL 1)
-    elseif(NOT LLVM_ENABLE_LIBCXX)
-      # Otherwise, test that we aren't using too old of a version of libstdc++
-      # with the Clang compiler. This is tricky as there is no real way to
-      # check the version of libstdc++ directly. Instead we test for a known
-      # bug in libstdc++4.6 that is fixed in libstdc++4.7.
-      set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
-      set(OLD_CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES})
-      set(CMAKE_REQUIRED_FLAGS "-std=c++0x")
-      check_cxx_source_compiles("
-#include <atomic>
-std::atomic<float> x(0.0f);
-int main() { return (float)x; }"
-        LLVM_NO_OLD_LIBSTDCXX)
-      if(NOT LLVM_NO_OLD_LIBSTDCXX)
-        message(FATAL_ERROR "Host Clang must be able to find libstdc++4.7 or newer!")
-      endif()
-      set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
-      set(CMAKE_REQUIRED_LIBRARIES ${OLD_CMAKE_REQUIRED_LIBRARIES})
-    endif()
-  elseif(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
-    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 18.0)
-      message(FATAL_ERROR "Host Visual Studio must be at least 2013")
-    elseif(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 18.0.31101)
-      message(WARNING "Host Visual Studio should at least be 2013 Update 4 (MSVC 18.0.31101)"
-        "  due to miscompiles from earlier versions")
-    endif()
-  endif()
-endif()
 
 if (CMAKE_LINKER MATCHES "lld-link.exe")
   # Pass /MANIFEST:NO so that CMake doesn't run mt.exe on our binaries.  Adding