[libc][bazel] Enable software prefetching for memset (#108860)

This will affect only Bazel configuration for now.

Author: gchatelet

utils/bazel/llvm-project-overlay/libc/libc_configure_options.bzl

@@ -25,7 +25,7 @@ LIBC_CONFIGURE_OPTIONS = [
     # "LIBC_COPT_MEMCPY_USE_EMBEDDED_TINY",
     # "LIBC_COPT_MEMCPY_X86_USE_REPMOVSB_FROM_SIZE",
     # "LIBC_COPT_MEMCPY_X86_USE_SOFTWARE_PREFETCHING",
-    # "LIBC_COPT_MEMSET_X86_USE_SOFTWARE_PREFETCHING",
+    "LIBC_COPT_MEMSET_X86_USE_SOFTWARE_PREFETCHING",
 
     # Documentation in libc/docs/dev/printf_behavior.rst
     # "LIBC_COPT_PRINTF_CONV_ATLAS",