[libc] Allow hermetic timing if the `clock` function is built (#71092)

Summary:
This patch fixes some code duplication on the GPU. The GPU build wanted
to enable timing for hermetic tests so it built some special case
handling into the test suite. Now that `clock` is supported on the
target we can simply link against the external interface. Because we
include `clock.h` for the CLOCKS_PER_SEC macro we remap the C entrypoint
to the internal one if it ends up called. This should allow hermetic
tests to run with timing if it is supported.

1 files changed, 6 insertions, 0 deletions

diff --git a/libc/cmake/modules/LLVMLibCTestRules.cmake b/libc/cmake/modules/LLVMLibCTestRules.cmake
index fc66c12..f7ca6a2 100644
--- a/libc/cmake/modules/LLVMLibCTestRules.cmake
+++ b/libc/cmake/modules/LLVMLibCTestRules.cmake
@@ -636,6 +636,12 @@ function(add_libc_hermetic_test test_name)
       libc.src.string.memset
       libc.src.__support.StringUtil.error_to_string
   )
+
+  if(TARGET libc.src.time.clock)
+    # We will link in the 'clock' implementation if it exists for test timing.
+    list(APPEND fq_deps_list libc.src.time.clock)
+  endif()
+
   list(REMOVE_DUPLICATES fq_deps_list)
 
   # TODO: Instead of gathering internal object files from entrypoints,