Look for FileCheck for running lit tests, too

Use of grep in `lit` RUN lines is deprecated:
https://llvm.org/docs/TestingGuide.html#writing-new-regression-tests

Using grep leads to really unhelpful failure output (it literally
just says "the test failed"). FileCheck is much more helpful, and
distributed with LLVM on most distros anyway, so this extra
dependency shouldn't prove problematic.

hipamd/hipify-clang/CMakeLists.txt

@@ -3,11 +3,12 @@ project(hipify-clang)
 
 option(HIPIFY_CLANG_TESTS "Build the tests for hipify-clang, if lit is installed" ON)
 
-# Disable the tests if `lit` is not installed.
+# Disable the tests if `lit` or `FileCheck` is not installed.
 find_program(LIT_COMMAND lit)
-if (NOT LIT_COMMAND)
+find_program(FILECHECK_COMMAND FileCheck)
+if (NOT LIT_COMMAND OR NOT FILECHECK_COMMAND)
     set(HIPIFY_CLANG_TESTS OFF CACHE INTERNAL "")
-    message(STATUS "hipify-clang's tests are not being built because `lit` is not installed.")
+    message(STATUS "hipify-clang's tests are not being built because `lit` or `FileCheck` could not be found.")
 endif()
 
 set(BUILD_HIPIFY_CLANG 0 CACHE INTERNAL "")