Add arm_neon.h and remove CMakeLists.txt

This commit copies `arm_neon.h` from `prebuilts/clang/host` and removes
unused `CMakeLists.txt`.

Bug: 111579848
Test: ./prebuilts/clang-tools/build-prebuilts.sh  # (on aosp/clang-tools
branch)

Change-Id: I7398cfc8f5399ea8b3fc838a41d8e294e71bc598
diff --git a/build-prebuilts.sh b/build-prebuilts.sh
index 98b33c2..f4dabf3 100755
--- a/build-prebuilts.sh
+++ b/build-prebuilts.sh
@@ -70,6 +70,8 @@
 
 # Copy clang headers
 cp -R "external/clang/lib/Headers" "${SOONG_OUT}/dist/clang-headers"
+cp "prebuilts/clang/host/${OS}-x86/clang-3289846/lib64/clang/3.8/include/arm_neon.h" "${SOONG_OUT}/dist/clang-headers"
+rm "${SOONG_OUT}/dist/clang-headers/CMakeLists.txt"
 
 # Package binaries and shared libs
 (