Correct Clang version detection and support for multiple prefix paths.

Bumps cmake minimum version to 3.7 for version comparison operator.

Previously the Clang cmake project version strings were used.  These
are not defined if the clang cmake project has not been loaded.
We should use CMAKE_CXX_COMPILER_VERSION to check the version when
only the compiler binary is redirected and the project files are
not available.

Also adjust device libs lookup logic to handle multiple paths in
CMAKE_PREFIX_PATH.

Change-Id: I67b6958d8241685cd6c3a0af68507c9fdc6331ef

runtime/hsa-runtime/image/blit_src/CMakeLists.txt

@@ -40,7 +40,7 @@
 ##
 ################################################################################
 
-cmake_minimum_required ( VERSION 3.5.0 )
+cmake_minimum_required ( VERSION 3.7 )
 
 # Flag to abort before executing after default initialization of cache variables
 set (QUIT 0)
@@ -49,15 +49,20 @@ set (QUIT 0)
 find_package(Clang REQUIRED HINTS ${CMAKE_INSTALL_PREFIX}/llvm ${CMAKE_PREFIX_PATH}/llvm PATHS /opt/rocm/llvm )
 
 # Device libs doesn't support find_package yet.
-# FIXME: HINTS should not use CMAKE_INSTALL_PREFIX
+set(PREFIX_HINTS "")
+foreach(hint "/amdgcn/bitcode" "/lib/bitcode" "/lib/x86_64/bitcode")
+  foreach(path ${CMAKE_PREFIX_PATH})
+    string(APPEND path ${hint})
+    list(APPEND PREFIX_HINTS ${path})
+  endforeach(path)
+endforeach(hint)
+
 get_include_path(BITCODE_DIR "Bitcode library path" RESULT FOUND NAMES "opencl.bc" "opencl.amdgcn.bc"
   HINTS
     "${CMAKE_INSTALL_PREFIX}/amdgcn/bitcode"
     "${CMAKE_INSTALL_PREFIX}/lib/bitcode"
     "${CMAKE_INSTALL_PREFIX}/lib/x86_64/bitcode"
-    "${CMAKE_PREFIX_PATH}/amdgcn/bitcode"
-    "${CMAKE_PREFIX_PATH}/lib/bitcode"
-    "${CMAKE_PREFIX_PATH}/lib/x86_64/bitcode"
+    "${PREFIX_HINTS}"
   PATHS
     "/opt/rocm/amdgcn/bitcode"
     "/opt/rocm/lib/bitcode"