[libc][math][c23] Temporarily disable modff16 on AArch64 (#94972)

See Buildbot failure:
https://lab.llvm.org/buildbot/#/builders/138/builds/67428.

libc/config/linux/aarch64/entrypoints.txt

diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index 50e0a6d..8863749 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -526,7 +526,7 @@
     libc.src.math.logbf16
     libc.src.math.lrintf16
     libc.src.math.lroundf16
-    libc.src.math.modff16
+    # libc.src.math.modff16
     libc.src.math.nanf16
     libc.src.math.nearbyintf16
     libc.src.math.nextafterf16