kernel: Clean headers installed in uapi/asm as well

* Unlike on ARM64, devices building ARM32 installs the signal.h to
  uapi/asm. Include this possible variation to workaround conflicts
  with bionic.

Change-Id: If8e334dfadb544ac3d4256f6738780c797b6cccc

Author: Khalvat-M

tools/clean_headers.sh

@@ -4,4 +4,5 @@ set -eu
 export ANDROID_BUILD_TOP="$PWD"
 
 ./bionic/libc/kernel/tools/clean_header.py -u \
+    "$1/usr/include/asm/signal.h" \
     "$1/usr/include/asm-generic/signal.h"