CMakeList: Remove the CLANG_VERSION_STRING check

It appears to be undefined for me.
Let Kokoro decide if it is required.

Change-Id: I0052703552dd0727e6d3dc12f7947ce06faee5f6
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/29054
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 82baf74..1894499 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -232,8 +232,7 @@
     set_cpp_flag("-Werror=missing-braces")
     set_cpp_flag("-fno-exceptions")
 
-    if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
-       CLANG_VERSION_STRING VERSION_GREATER_EQUAL 5)
+    if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
         set_cpp_flag("-Werror=unused-lambda-capture")
         set_cpp_flag("-Werror=string-conversion")
     endif()