[MLIR][CMake] Suppress -Wpass-failed warning

libstdc++15 makes use of an unroll pragma inside std::find_if(). This
produces a warning if clang fails to unroll the loop. As this pragma is
outside of our control, suppress the warning.

Author: nikic

mlir/CMakeLists.txt

@@ -110,6 +110,12 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
   endif()
 endif()
 
+# libstdc++15 makes use of an unroll pragma inside std::find_if(). This
+# produces a warning if clang fails to unroll the loop. As this pragma is
+# outside of our control, suppress the warning.
+check_cxx_compiler_flag("-Wno-pass-failed" CXX_SUPPORTS_WNO_PASS_FAILED)
+append_if(CXX_SUPPORTS_WNO_PASS_FAILED "-Wno-pass-failed" CMAKE_CXX_FLAGS)
+
 # Installing the headers and docs needs to depend on generating any public
 # tablegen'd targets.
 # mlir-generic-headers are dialect-independent.