[libc] disable strfroml entrypoint on aarch64 (llvm#101854)

Disable `strfroml` entrypoint on aarch64 to please clang-11 buildbots.
Detailed in llvm#101846. This is
not a fix for llvm#101846 so I will keep the issue open until our buildbot
is updated or other mitigation is applied.

libc/config/linux/aarch64/entrypoints.txt

@@ -189,7 +189,8 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdlib.srand
     libc.src.stdlib.strfromd
     libc.src.stdlib.strfromf
-    libc.src.stdlib.strfroml
+    # TODO: long double support is buggy with clang-11. Re-enable when buildbots are upgraded.
+    # libc.src.stdlib.strfroml
     libc.src.stdlib.strtod
     libc.src.stdlib.strtof
     libc.src.stdlib.strtol