Clang: Find version-suffixed LLVM/Clang binutils

Debian renames all LLVM/Clang binaries with a version suffix to allow
multiple versions to be installed at the same time.  While there is a
version-agnostic package that adds a symlink to provide the standard
binary names, if only the versioned packages are installed, binaries
must be found as `binary-x.y`.  In any case, using the same version of
the `binutils` as the compiler seems better.

Modules/Compiler/Clang-FindBinUtils.cmake

@@ -2,6 +2,12 @@ if(NOT DEFINED _CMAKE_PROCESSING_LANGUAGE OR _CMAKE_PROCESSING_LANGUAGE STREQUAL
   message(FATAL_ERROR "Internal error: _CMAKE_PROCESSING_LANGUAGE is not set")
 endif()
 
+# Debian:
+# * /usr/bin/llvm-ar-4.0
+# * /usr/bin/llvm-ranlib-4.0
+string(REGEX MATCH "^([0-9]+\\.[0-9]+)" __version_x_y
+    "${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_VERSION}")
+
 # Try to find tools in the same directory as Clang itself
 get_filename_component(__clang_hint_1 "${CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER}" REALPATH)
 get_filename_component(__clang_hint_1 "${__clang_hint_1}" DIRECTORY)
@@ -12,6 +18,7 @@ set(__clang_hints ${__clang_hint_1} ${__clang_hint_2})
 
 # http://manpages.ubuntu.com/manpages/precise/en/man1/llvm-ar.1.html
 find_program(CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_AR NAMES
+    "${_CMAKE_TOOLCHAIN_PREFIX}llvm-ar-${__version_x_y}"
     "${_CMAKE_TOOLCHAIN_PREFIX}llvm-ar"
     HINTS ${__clang_hints}
     DOC "LLVM archiver"
@@ -20,6 +27,7 @@ mark_as_advanced(CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_AR)
 
 # http://manpages.ubuntu.com/manpages/precise/en/man1/llvm-ranlib.1.html
 find_program(CMAKE_${_CMAKE_PROCESSING_LANGUAGE}_COMPILER_RANLIB NAMES
+    "${_CMAKE_TOOLCHAIN_PREFIX}llvm-ranlib-${__version_x_y}"
     "${_CMAKE_TOOLCHAIN_PREFIX}llvm-ranlib"
     HINTS ${__clang_hints}
     DOC "Generate index for LLVM archive"